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...
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 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 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...
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 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.
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Papers by Donald W. Setser