ChemInform Abstract Die Geschwindigkeiten der Bildung von HCl und HF bei den Reaktionen von Hmit ... more ChemInform Abstract Die Geschwindigkeiten der Bildung von HCl und HF bei den Reaktionen von Hmit ICl bzw. ClF werden relativ zu der Geschwindigkeit der HCl-Bildung aus Hund C12 im Strömungsreaktor anhand der Intensität der IR-Chemilumineszenz der Produkte bestimmt, ebenso die Geschwindigkeit der HF-Bildung bei der' Reaktion von H mit F2 relativ zu der Geschwindigkeit der HCl-Bildung aus Hund C12.
Publication costs assisted by the Department of Defense Nonequilibrium vibrational distributions ... more Publication costs assisted by the Department of Defense Nonequilibrium vibrational distributions of CO+(A2n,u'=0-6), CS(A1rI,u'=&5), and Cz(A3TI,u '=M) were prepared by collisional processes in a 300-I< helium flowing-afterglow apparatus. The vibrational band intensities of the electronic emission systems were used to obtain the steady-state vibrational distributions from 0.8 to 15 torr. Extensive vibrational relaxation by collisions with He was observed for CO"(A) and CS(A), but not for C,(A), over this pressure range, Electronic quenching of CS(A) probably is competitive with vibrational relaxation, even in helium. The data were fitted to relaxation models based upon Au = 1 collisional transitions by using the steady-state master equation formulation. The Au = 1 relaxation cross sections for CO+(A) and CS(A) with He are in the range of 0.01 of the gas kinetic values. The upper limit to the 4 u =-1 relaxation cross section for C,(A) is 5 X of the gas kinetic value. Studies of the relaxation of CS(A'n) in Ar were attempted, but electronic quenching appeared to dominate over vibrational relaxation. These results are compared to vibrational-translational relaxation of other electronically excited states.
The vibrational, and in some cases rotational, populations of the CN (A 2Πi) and (B 2Σ+) states p... more The vibrational, and in some cases rotational, populations of the CN (A 2Πi) and (B 2Σ+) states produced by the dissociative excitation reactions of metastable argon and xenon atoms with HCN, ICN, and BrCN have been measured. Emission from the D, E, and F states of CN were observed from Ar(3P0,2) with BrCN. Anomalously high intensities from perturbed rotational levels of CN (B 2Σ+; v′ = 0, 11, 14) were found, and only the perturbed levels are produced from CNBr and CNI. The interaction of metastable argon atoms with BrCN and ICN gave excitation to v′ = 20 of CN (B 2Σ+) with a population inversion for v′ > 11 relative to lower levels. Extremely high rotational excitation of CN (B 2Σ+; v′ = 0, 1, 2) resulted from the interaction of Xe(3P2) with BrCN and ICN. The spectroscopic observations provide extensive detail and illustrate the complexity of these dissociative excitation reactions. In addition to a short discussion of the mechanism of interaction between the metastable atoms an...
HF infrared chemiluminescence from the reactions of F atoms with HCl, HBr, and HI was used to ass... more HF infrared chemiluminescence from the reactions of F atoms with HCl, HBr, and HI was used to assign vibrational–rotational populations of the HF product. Experiments were done in both a cold-wall, arrested vibrational–rotational relaxation apparatus and in a fast-flow, arrested vibrational relaxation apparatus. Since the total HF formation rate constants are known for these reactions, absolute 300 K rate constants for formation of HFvJ are established. The mean vibrational energy disposal to HF including estimates for HF (v=0) is <fV≳HCl=0.51, <fV≳HBr=0.59 and <fV≳HI=0.59. The mean HF rotational energy decreased from 0.18 to 0.12 in the HCl–HI series. The <fV+fR≳ sum is virtually constant for the three reactions, but <fV≳ does increase slightly as the reactions become more exoergic. The HBr reaction yields ∼10% Br(2P1/2), the upper spin–orbit state; but I(2P1/2) is not formed from HI. Independent work by Nip and Clyne on the HCl reaction suggest that Cl(2P1/2) also i...
The infrared chemiluminescence of vibrationally excited H2O and HDO from the highly exothermic re... more The infrared chemiluminescence of vibrationally excited H2O and HDO from the highly exothermic reactions of OH and OD radicals with HI and GeH4 was observed in the 2200–5500 cm−1 range. The experiments utilized a fast-flow reactor with 0.3–1 Torr of Ar carrier gas at 300 K; the OH(OD) radicals were produced via the H(D)+NO2 reaction and the H or D atoms were generated by a discharge in a H2(D2)/Ar mixture. The H2O and HOD vibrational distributions were determined by computer simulation of the emission spectra in the 2200–3900 cm−1 range. The total vibrational energy released to H2O and HOD molecules is, respectively, 〈fv〉=0.36 and 0.41 from HI and 〈fv〉=0.46 and 0.51 from GeH4. These values are significantly smaller than for the reactions of OH and OD with HBr, 〈fv〉=0.61 and 0.65. The populations of the O–H stretching vibration of HOD and the collisionally coupled ν1 and ν3 stretching modes of H2O decrease with increasing vibrational energy. In contrast, the vibrational distribution ...
The quasiclassical trajectory (QCT) method was used to study the dynamics of the OH(X 2Π) and OD(... more The quasiclassical trajectory (QCT) method was used to study the dynamics of the OH(X 2Π) and OD(X 2Π)+HBr chemical reactions on an empirical potential energy surface (PES). The main emphasis in the calculation was the vibrational energy distributions of H2O (and HDO) and the magnitude and temperature dependence of the rate constant. However, this PES also serves as a generic model for the dynamics of direct H atom abstraction by OH radicals. Since this PES has no formal potential energy barrier, variational transition-state theory was used to obtain rate constants for comparison with the QCT calculations and experimental results. The parameters of the potential energy surface were adjusted to obtain better agreement with the experimentally measured fraction of H2O vibrational energy, 〈fV(H2O)〉=0.6, without significantly changing the entrance channel. No isotope effect for the partition of energy to H2O vs HOD was found. Analysis of the trajectories indicates that the reactant OH(OD...
The conversion of Xe(6s[3/2],) metaatable atoms to Xe(6s'[ 1/2]J metaatable atoms has been succes... more The conversion of Xe(6s[3/2],) metaatable atoms to Xe(6s'[ 1/2]J metaatable atoms has been successfully accomplished in a flow reactor by optical pumping in He carrier gas The Xe(3PP,) concentration was depleted by a factor of 8-10 with 12% conversion to the Xe ('PO) concentration. The propensity for conservation of the Xe+ (*Pljl) ion-core is negligible in the reactions of Xe('Po) with halogen-containing molecules (RX), except for F2 and Br2. The emission spectra and the product branching ratios for XeX(B) formation from the reactions of Xe(3Po) with RX molecules are similar to those from reactions of Xe(6p) atoms, which suggests a coupling between the Xe(6s') tRX and the Xe(6p) t RX potentials in the entrance channel.
Infrared chemiluminescence from HF under conditions of arrested relaxation has been used to measu... more Infrared chemiluminescence from HF under conditions of arrested relaxation has been used to measure steady-state vibrational and rotational population distributions from the reaction of fluorine atoms with H2C0, CD3CH0, C6H5CH0, CH30CH3, and H202. For F + HzCO the fraction of energy released as HFt vibrational, (f~) , and rotational, (f~) , energy was 10.43 and-0.12, respectively. The highest H F t ,~ level corresponded to the maximum permitted by the thermochemistry, even though HCO is a stabilized radical. In contrast, the highest HFt,J levels from F + CHBCHO (CD3CHO) and CGH&HO were less than the thermochemical limits, which suggests that these radicals relax to the most stable geometry on a slower time scale than the HCO radical, thus making the stabilization energy unavailable to HFt. Abstraction of H from the aldehyde position appears to favor a higher (f R) than most other C-H bonds. In seeking an explanation for this, the reactions with (CHJ20, which also favors high (f R) , and Hz02, which has similar thermochemistry to H2C0, has been reinvestigated. The CH30CH3 reaction also yields a stabilized radical and the stabilization energy was not freely available to HFt. The CH30CH3 reaction could be studied under highly arrested conditions and estimation of the initial rotational distributions are presented. The energy disposal characteristics of these reactions are interpreted and discussed with the aid of surprisal analyses. A difference between the rotational energy disposal for the F + HX and F + HR (R = polyatomic) reactions is tentatively identified.
A flow reactor has been used to measure the room temperature rate constants for quenching of NF(a... more A flow reactor has been used to measure the room temperature rate constants for quenching of NF(aIA) by molecules containing the N F bond and by SiF4, HNCO, and NCO. The quenching rate constants decrease in the series NF(X), N2F4, NF2, and NF3. The rate constant for NF(X) is (3 f 1) X cm3 molecule-' s-l, which is smaller than the bimolecular self-destruction rate constant of NF(a). The quenching rate was so slow for NF3 that only an upper limit to the rate constant, 1.6 X 1O-I' cm3 molecule-' s-I, could be measured. The quenching constant for SiF4 is also small,-1.4 X 1 W cm3 molecule-' s-l. The rate constants for HNCO and NCO were measured because these molecules were utilized in the generation of NF(X); estimates for their rate constants are (4.5 f 1.0) X lO-I3 and (7.0 f 1.0) X 10-13 cm3 molecule-' s-I. The quenching constants for HNCO and NCO are consistent with those for other carbonyl-containing molecules.
The reaction of excess F atoms with HN, in a halocarbon-coated flow reactor has been used to gene... more The reaction of excess F atoms with HN, in a halocarbon-coated flow reactor has been used to generate and study the quenching reactions of NF(a'A,v'=O) at 300 K. Fifteen reagents, selected to represent a variety of chemical interactions, were tested in order to provide a survey of quenching rate constants that could be compared to O,(a'A,) and NH(a'A). A range of rate constants was found which varied from-1.0 X IO-'] 6171, s-' for N(CH,), to-1.0 X (3117, s-I for N2, H2, and NO. The NF(a'A) molecule is much less reactive than NH(a'A), and it seems to more closely resemble O,(alA,). However, the quenching rate constants for NF(a'A) generally are larger than for 02(a1A) and show a greater variation from one reagent being a small component of the total self-quenching reaction. to another. The self-quenching rate constant for NF(alA) is (2.2 k 1.2) X 10-7 cm3 s-I with energy pooling to give NF(b'Z+)
Krypton chloride and krypton fluoride molecules were formed by the Kr(³Pâ) sensitization reacti... more Krypton chloride and krypton fluoride molecules were formed by the Kr(³Pâ) sensitization reaction with Clâ or Fâ in variable pressures (up to 5 atm) of Ar, Nâ, and CFâ buffer gases at 300 and 230 K. Less extensive experiments also were done in He and Ne. The high-pressure (equilibrium) KrF(C)/KrF(B) and KrCl(C)/KrCl(B) ratios were observed in order to assign the energy separation of the C and B states. The KrF(B,C) + 2Ar rate constant for ArKrF{sup *} formation was assigned as (8 {plus minus} 3) à 10â»Â³Â³ cmⶠmoleculeâ»Â² sâ»Â¹ at 300 K; a slight larger value was estimated for formation of ArKrCl{sup *}.
The vibrational energy disposal to OH and relative rate constants have been measured for the 0 + ... more The vibrational energy disposal to OH and relative rate constants have been measured for the 0 + HI and GeH, reactions and for the H + NOz and CIOz reactions. The experiments were done in a flowing afterglow apparatus which gives arrested vibrational distributions as shown by comparisons of the OH(u) distribution from H + NOz with other data in the literature. The energy disposal pattern for the 0 atom reactions closely resembles that for F (or C1) atom reactions. Comparison of the relative emission intensities from H + NOz and H + Clz and the accepted rate constants for the reactions permits a selection to be made for the better vibrational OH u'-* u'-1 Einstein coefficients. Emission from NO was observed from the H + NOz reaction confirming predictions that NO is involved in the energy disposal.
The infrared chemiluminescence from vibrationally excited H20 molecules in the 3200-4000 cm-' ran... more The infrared chemiluminescence from vibrationally excited H20 molecules in the 3200-4000 cm-' range was observed from the unimolecular decomposition of C2HsOH" in a fast flow reactor coupled with a Fourier transform infrared spectrometer. Activated ethanol molecules were generated via the successive reactions H + CHzICHzOH-HI + CH2CH20H and H + CH2CH20H-CH3CHzOH*; the excitation energy of C2Hs-OH is about 100 kcal mol-'. Simulation of the experimental spectrum was made using the available absorption intensities for V I , 2v2, and v3 bands of H20. The main contributions are from the (0~21)-. (0~20) and (0~2 2)-(0~21) transitions with extensively excited bending vibrations. The energy distribution for H20 agrees with the general picture for the dynamics of four-centered elimination reactions of halo-substituted alkanes for which only a small fraction of the potential energy is released as vibrational energy to the eliminated product. A b initio and RRKM calculations have been carried out in order to compare the statistical reaction probabilities for the H20 + C Z~, C2H5 + OH, and CH3 + CH20H unimolecular decomposition pathways of ethanol. The ab initio results suggest that the threshold energy for H20 elimination from ethanol is 1 6 7 kcal mol-'.
The room-temperature gas-phase recombination of CH2F and CD2Cl radicals was used to prepare CH2FC... more The room-temperature gas-phase recombination of CH2F and CD2Cl radicals was used to prepare CH2FCD2Cl molecules with 91 kcal mol(-1) of vibrational energy. Three unimolecular processes are in competition with collisional deactivation of CH2FCD2Cl; HCl and DF elimination to give CHF═CD2 and CH2═CDCl plus isomerization to give CH2ClCD2F by the interchange of F and Cl atoms. The Cl/F interchange reaction was observed, and the rate constant was assigned from measurement of CHCl═CD2 as a product, which is formed by HF elimination from CH2ClCD2F. These experiments plus previously published results from chemically activated CH2ClCH2F and electronic structure and RRKM calculations for the kinetic-isotope effects permit assignment of the three rate constants for CH2FCD2Cl (and for CH2ClCD2F). The product branching ratio for the interchange reaction versus elimination is 0.24 ± 0.04. Comparison of the experimental rate constant with the RRKM calculated rate constant permitted the assignment of a threshold energy of 62 ± 3 kcal mol(-1) for this type-1 dyotropic rearrangement. On the basis of electronic structure calculations, the nature of the transition state for the rearrangement reaction is discussed. The radical recombination reactions in the chemical system also generate vibrationally excited CD2ClCD2Cl and CH2FCH2F molecules, and the rate constants for DCl and HF elimination were measured in order to confirm that the photolysis of CD2ClI and (CH2F)2CO mixtures was giving reliable data for CH2FCD2Cl.
The infrared chemiluminescence of H 2 O and HOD molecules formed from the room-temperature reacti... more The infrared chemiluminescence of H 2 O and HOD molecules formed from the room-temperature reactions of OH and OD radicals with H 2 S, CH 3 SCH 3 , and CH 3 SH was recorded by viewing a fast-flow reactor with a Fourier transform spectrometer. Nascent vibrational distributions of the H 2 O and HDO product molecules were obtained by computer simulation of the infrared spectra. According to our assignments for the V 3) 0 populations, the vibrational distributions of HDO from the H 2 S and CH 3 SCH 3 reactions were inverted in the O-H stretching mode with a maximum in V 3) 2 and V 3) 1, respectively, and the fraction of the available energy released as vibrational energy is 〈f V 〉 ≈ 0.6 with ∼25-30% of the vibrational energy in the bending coordinate. The reaction with CH 3 SH gives a HOD vibrational distribution that declines with increased V 3 ; 〈f V 〉 is only ≈0.4, but 40% of the vibrational energy is in the bending mode. For each reaction, the vibrational distributions for H 2 O closely resemble those for HOD, after allowance is made for the collision-induced equilibration between the ν 1 and ν 3 modes of H 2 O and the ν 1 and 2ν 2 modes of HOD. The reduced vibrational energy disposal to H 2 O and HOD from CH 3 SH is taken as evidence for a mechanism that differs from the direct abstraction process for the H 2 S and CH 3 SCH 3 reactions. These results are analyzed using information theory, and they also are compared with the data from similar reactions of hydroxyl radicals and F atoms. Secondary reactions of the sulfur-containing primary radicals (SH, CH 3 S, and CH 3 SCH 2) with NO 2 and NO are discussed.
ChemInform Abstract Die Geschwindigkeiten der Bildung von HCl und HF bei den Reaktionen von Hmit ... more ChemInform Abstract Die Geschwindigkeiten der Bildung von HCl und HF bei den Reaktionen von Hmit ICl bzw. ClF werden relativ zu der Geschwindigkeit der HCl-Bildung aus Hund C12 im Strömungsreaktor anhand der Intensität der IR-Chemilumineszenz der Produkte bestimmt, ebenso die Geschwindigkeit der HF-Bildung bei der' Reaktion von H mit F2 relativ zu der Geschwindigkeit der HCl-Bildung aus Hund C12.
Publication costs assisted by the Department of Defense Nonequilibrium vibrational distributions ... more Publication costs assisted by the Department of Defense Nonequilibrium vibrational distributions of CO+(A2n,u'=0-6), CS(A1rI,u'=&5), and Cz(A3TI,u '=M) were prepared by collisional processes in a 300-I< helium flowing-afterglow apparatus. The vibrational band intensities of the electronic emission systems were used to obtain the steady-state vibrational distributions from 0.8 to 15 torr. Extensive vibrational relaxation by collisions with He was observed for CO"(A) and CS(A), but not for C,(A), over this pressure range, Electronic quenching of CS(A) probably is competitive with vibrational relaxation, even in helium. The data were fitted to relaxation models based upon Au = 1 collisional transitions by using the steady-state master equation formulation. The Au = 1 relaxation cross sections for CO+(A) and CS(A) with He are in the range of 0.01 of the gas kinetic values. The upper limit to the 4 u =-1 relaxation cross section for C,(A) is 5 X of the gas kinetic value. Studies of the relaxation of CS(A'n) in Ar were attempted, but electronic quenching appeared to dominate over vibrational relaxation. These results are compared to vibrational-translational relaxation of other electronically excited states.
The vibrational, and in some cases rotational, populations of the CN (A 2Πi) and (B 2Σ+) states p... more The vibrational, and in some cases rotational, populations of the CN (A 2Πi) and (B 2Σ+) states produced by the dissociative excitation reactions of metastable argon and xenon atoms with HCN, ICN, and BrCN have been measured. Emission from the D, E, and F states of CN were observed from Ar(3P0,2) with BrCN. Anomalously high intensities from perturbed rotational levels of CN (B 2Σ+; v′ = 0, 11, 14) were found, and only the perturbed levels are produced from CNBr and CNI. The interaction of metastable argon atoms with BrCN and ICN gave excitation to v′ = 20 of CN (B 2Σ+) with a population inversion for v′ > 11 relative to lower levels. Extremely high rotational excitation of CN (B 2Σ+; v′ = 0, 1, 2) resulted from the interaction of Xe(3P2) with BrCN and ICN. The spectroscopic observations provide extensive detail and illustrate the complexity of these dissociative excitation reactions. In addition to a short discussion of the mechanism of interaction between the metastable atoms an...
HF infrared chemiluminescence from the reactions of F atoms with HCl, HBr, and HI was used to ass... more HF infrared chemiluminescence from the reactions of F atoms with HCl, HBr, and HI was used to assign vibrational–rotational populations of the HF product. Experiments were done in both a cold-wall, arrested vibrational–rotational relaxation apparatus and in a fast-flow, arrested vibrational relaxation apparatus. Since the total HF formation rate constants are known for these reactions, absolute 300 K rate constants for formation of HFvJ are established. The mean vibrational energy disposal to HF including estimates for HF (v=0) is <fV≳HCl=0.51, <fV≳HBr=0.59 and <fV≳HI=0.59. The mean HF rotational energy decreased from 0.18 to 0.12 in the HCl–HI series. The <fV+fR≳ sum is virtually constant for the three reactions, but <fV≳ does increase slightly as the reactions become more exoergic. The HBr reaction yields ∼10% Br(2P1/2), the upper spin–orbit state; but I(2P1/2) is not formed from HI. Independent work by Nip and Clyne on the HCl reaction suggest that Cl(2P1/2) also i...
The infrared chemiluminescence of vibrationally excited H2O and HDO from the highly exothermic re... more The infrared chemiluminescence of vibrationally excited H2O and HDO from the highly exothermic reactions of OH and OD radicals with HI and GeH4 was observed in the 2200–5500 cm−1 range. The experiments utilized a fast-flow reactor with 0.3–1 Torr of Ar carrier gas at 300 K; the OH(OD) radicals were produced via the H(D)+NO2 reaction and the H or D atoms were generated by a discharge in a H2(D2)/Ar mixture. The H2O and HOD vibrational distributions were determined by computer simulation of the emission spectra in the 2200–3900 cm−1 range. The total vibrational energy released to H2O and HOD molecules is, respectively, 〈fv〉=0.36 and 0.41 from HI and 〈fv〉=0.46 and 0.51 from GeH4. These values are significantly smaller than for the reactions of OH and OD with HBr, 〈fv〉=0.61 and 0.65. The populations of the O–H stretching vibration of HOD and the collisionally coupled ν1 and ν3 stretching modes of H2O decrease with increasing vibrational energy. In contrast, the vibrational distribution ...
The quasiclassical trajectory (QCT) method was used to study the dynamics of the OH(X 2Π) and OD(... more The quasiclassical trajectory (QCT) method was used to study the dynamics of the OH(X 2Π) and OD(X 2Π)+HBr chemical reactions on an empirical potential energy surface (PES). The main emphasis in the calculation was the vibrational energy distributions of H2O (and HDO) and the magnitude and temperature dependence of the rate constant. However, this PES also serves as a generic model for the dynamics of direct H atom abstraction by OH radicals. Since this PES has no formal potential energy barrier, variational transition-state theory was used to obtain rate constants for comparison with the QCT calculations and experimental results. The parameters of the potential energy surface were adjusted to obtain better agreement with the experimentally measured fraction of H2O vibrational energy, 〈fV(H2O)〉=0.6, without significantly changing the entrance channel. No isotope effect for the partition of energy to H2O vs HOD was found. Analysis of the trajectories indicates that the reactant OH(OD...
The conversion of Xe(6s[3/2],) metaatable atoms to Xe(6s'[ 1/2]J metaatable atoms has been succes... more The conversion of Xe(6s[3/2],) metaatable atoms to Xe(6s'[ 1/2]J metaatable atoms has been successfully accomplished in a flow reactor by optical pumping in He carrier gas The Xe(3PP,) concentration was depleted by a factor of 8-10 with 12% conversion to the Xe ('PO) concentration. The propensity for conservation of the Xe+ (*Pljl) ion-core is negligible in the reactions of Xe('Po) with halogen-containing molecules (RX), except for F2 and Br2. The emission spectra and the product branching ratios for XeX(B) formation from the reactions of Xe(3Po) with RX molecules are similar to those from reactions of Xe(6p) atoms, which suggests a coupling between the Xe(6s') tRX and the Xe(6p) t RX potentials in the entrance channel.
Infrared chemiluminescence from HF under conditions of arrested relaxation has been used to measu... more Infrared chemiluminescence from HF under conditions of arrested relaxation has been used to measure steady-state vibrational and rotational population distributions from the reaction of fluorine atoms with H2C0, CD3CH0, C6H5CH0, CH30CH3, and H202. For F + HzCO the fraction of energy released as HFt vibrational, (f~) , and rotational, (f~) , energy was 10.43 and-0.12, respectively. The highest H F t ,~ level corresponded to the maximum permitted by the thermochemistry, even though HCO is a stabilized radical. In contrast, the highest HFt,J levels from F + CHBCHO (CD3CHO) and CGH&HO were less than the thermochemical limits, which suggests that these radicals relax to the most stable geometry on a slower time scale than the HCO radical, thus making the stabilization energy unavailable to HFt. Abstraction of H from the aldehyde position appears to favor a higher (f R) than most other C-H bonds. In seeking an explanation for this, the reactions with (CHJ20, which also favors high (f R) , and Hz02, which has similar thermochemistry to H2C0, has been reinvestigated. The CH30CH3 reaction also yields a stabilized radical and the stabilization energy was not freely available to HFt. The CH30CH3 reaction could be studied under highly arrested conditions and estimation of the initial rotational distributions are presented. The energy disposal characteristics of these reactions are interpreted and discussed with the aid of surprisal analyses. A difference between the rotational energy disposal for the F + HX and F + HR (R = polyatomic) reactions is tentatively identified.
A flow reactor has been used to measure the room temperature rate constants for quenching of NF(a... more A flow reactor has been used to measure the room temperature rate constants for quenching of NF(aIA) by molecules containing the N F bond and by SiF4, HNCO, and NCO. The quenching rate constants decrease in the series NF(X), N2F4, NF2, and NF3. The rate constant for NF(X) is (3 f 1) X cm3 molecule-' s-l, which is smaller than the bimolecular self-destruction rate constant of NF(a). The quenching rate was so slow for NF3 that only an upper limit to the rate constant, 1.6 X 1O-I' cm3 molecule-' s-I, could be measured. The quenching constant for SiF4 is also small,-1.4 X 1 W cm3 molecule-' s-l. The rate constants for HNCO and NCO were measured because these molecules were utilized in the generation of NF(X); estimates for their rate constants are (4.5 f 1.0) X lO-I3 and (7.0 f 1.0) X 10-13 cm3 molecule-' s-I. The quenching constants for HNCO and NCO are consistent with those for other carbonyl-containing molecules.
The reaction of excess F atoms with HN, in a halocarbon-coated flow reactor has been used to gene... more The reaction of excess F atoms with HN, in a halocarbon-coated flow reactor has been used to generate and study the quenching reactions of NF(a'A,v'=O) at 300 K. Fifteen reagents, selected to represent a variety of chemical interactions, were tested in order to provide a survey of quenching rate constants that could be compared to O,(a'A,) and NH(a'A). A range of rate constants was found which varied from-1.0 X IO-'] 6171, s-' for N(CH,), to-1.0 X (3117, s-I for N2, H2, and NO. The NF(a'A) molecule is much less reactive than NH(a'A), and it seems to more closely resemble O,(alA,). However, the quenching rate constants for NF(a'A) generally are larger than for 02(a1A) and show a greater variation from one reagent being a small component of the total self-quenching reaction. to another. The self-quenching rate constant for NF(alA) is (2.2 k 1.2) X 10-7 cm3 s-I with energy pooling to give NF(b'Z+)
Krypton chloride and krypton fluoride molecules were formed by the Kr(³Pâ) sensitization reacti... more Krypton chloride and krypton fluoride molecules were formed by the Kr(³Pâ) sensitization reaction with Clâ or Fâ in variable pressures (up to 5 atm) of Ar, Nâ, and CFâ buffer gases at 300 and 230 K. Less extensive experiments also were done in He and Ne. The high-pressure (equilibrium) KrF(C)/KrF(B) and KrCl(C)/KrCl(B) ratios were observed in order to assign the energy separation of the C and B states. The KrF(B,C) + 2Ar rate constant for ArKrF{sup *} formation was assigned as (8 {plus minus} 3) à 10â»Â³Â³ cmⶠmoleculeâ»Â² sâ»Â¹ at 300 K; a slight larger value was estimated for formation of ArKrCl{sup *}.
The vibrational energy disposal to OH and relative rate constants have been measured for the 0 + ... more The vibrational energy disposal to OH and relative rate constants have been measured for the 0 + HI and GeH, reactions and for the H + NOz and CIOz reactions. The experiments were done in a flowing afterglow apparatus which gives arrested vibrational distributions as shown by comparisons of the OH(u) distribution from H + NOz with other data in the literature. The energy disposal pattern for the 0 atom reactions closely resembles that for F (or C1) atom reactions. Comparison of the relative emission intensities from H + NOz and H + Clz and the accepted rate constants for the reactions permits a selection to be made for the better vibrational OH u'-* u'-1 Einstein coefficients. Emission from NO was observed from the H + NOz reaction confirming predictions that NO is involved in the energy disposal.
The infrared chemiluminescence from vibrationally excited H20 molecules in the 3200-4000 cm-' ran... more The infrared chemiluminescence from vibrationally excited H20 molecules in the 3200-4000 cm-' range was observed from the unimolecular decomposition of C2HsOH" in a fast flow reactor coupled with a Fourier transform infrared spectrometer. Activated ethanol molecules were generated via the successive reactions H + CHzICHzOH-HI + CH2CH20H and H + CH2CH20H-CH3CHzOH*; the excitation energy of C2Hs-OH is about 100 kcal mol-'. Simulation of the experimental spectrum was made using the available absorption intensities for V I , 2v2, and v3 bands of H20. The main contributions are from the (0~21)-. (0~20) and (0~2 2)-(0~21) transitions with extensively excited bending vibrations. The energy distribution for H20 agrees with the general picture for the dynamics of four-centered elimination reactions of halo-substituted alkanes for which only a small fraction of the potential energy is released as vibrational energy to the eliminated product. A b initio and RRKM calculations have been carried out in order to compare the statistical reaction probabilities for the H20 + C Z~, C2H5 + OH, and CH3 + CH20H unimolecular decomposition pathways of ethanol. The ab initio results suggest that the threshold energy for H20 elimination from ethanol is 1 6 7 kcal mol-'.
The room-temperature gas-phase recombination of CH2F and CD2Cl radicals was used to prepare CH2FC... more The room-temperature gas-phase recombination of CH2F and CD2Cl radicals was used to prepare CH2FCD2Cl molecules with 91 kcal mol(-1) of vibrational energy. Three unimolecular processes are in competition with collisional deactivation of CH2FCD2Cl; HCl and DF elimination to give CHF═CD2 and CH2═CDCl plus isomerization to give CH2ClCD2F by the interchange of F and Cl atoms. The Cl/F interchange reaction was observed, and the rate constant was assigned from measurement of CHCl═CD2 as a product, which is formed by HF elimination from CH2ClCD2F. These experiments plus previously published results from chemically activated CH2ClCH2F and electronic structure and RRKM calculations for the kinetic-isotope effects permit assignment of the three rate constants for CH2FCD2Cl (and for CH2ClCD2F). The product branching ratio for the interchange reaction versus elimination is 0.24 ± 0.04. Comparison of the experimental rate constant with the RRKM calculated rate constant permitted the assignment of a threshold energy of 62 ± 3 kcal mol(-1) for this type-1 dyotropic rearrangement. On the basis of electronic structure calculations, the nature of the transition state for the rearrangement reaction is discussed. The radical recombination reactions in the chemical system also generate vibrationally excited CD2ClCD2Cl and CH2FCH2F molecules, and the rate constants for DCl and HF elimination were measured in order to confirm that the photolysis of CD2ClI and (CH2F)2CO mixtures was giving reliable data for CH2FCD2Cl.
The infrared chemiluminescence of H 2 O and HOD molecules formed from the room-temperature reacti... more The infrared chemiluminescence of H 2 O and HOD molecules formed from the room-temperature reactions of OH and OD radicals with H 2 S, CH 3 SCH 3 , and CH 3 SH was recorded by viewing a fast-flow reactor with a Fourier transform spectrometer. Nascent vibrational distributions of the H 2 O and HDO product molecules were obtained by computer simulation of the infrared spectra. According to our assignments for the V 3) 0 populations, the vibrational distributions of HDO from the H 2 S and CH 3 SCH 3 reactions were inverted in the O-H stretching mode with a maximum in V 3) 2 and V 3) 1, respectively, and the fraction of the available energy released as vibrational energy is 〈f V 〉 ≈ 0.6 with ∼25-30% of the vibrational energy in the bending coordinate. The reaction with CH 3 SH gives a HOD vibrational distribution that declines with increased V 3 ; 〈f V 〉 is only ≈0.4, but 40% of the vibrational energy is in the bending mode. For each reaction, the vibrational distributions for H 2 O closely resemble those for HOD, after allowance is made for the collision-induced equilibration between the ν 1 and ν 3 modes of H 2 O and the ν 1 and 2ν 2 modes of HOD. The reduced vibrational energy disposal to H 2 O and HOD from CH 3 SH is taken as evidence for a mechanism that differs from the direct abstraction process for the H 2 S and CH 3 SCH 3 reactions. These results are analyzed using information theory, and they also are compared with the data from similar reactions of hydroxyl radicals and F atoms. Secondary reactions of the sulfur-containing primary radicals (SH, CH 3 S, and CH 3 SCH 2) with NO 2 and NO are discussed.
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Papers by Donald W. Setser