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1-Phenylpyrrole has been identified by several authors as a molecule that displays twisted intramolecular charge-transfer (TICT) character in the condensed phase. However, Suzuka and coworkers, using single vibronic level dispersed... more
1-Phenylpyrrole has been identified by several authors as a molecule that displays twisted intramolecular charge-transfer (TICT) character in the condensed phase. However, Suzuka and coworkers, using single vibronic level dispersed fluorescence, observed no evidence of TICT activity in the gas phase. In this work, 1-phenylpyrrole is studied by the high resolution methods previously applied to DMABN to determine the extent of its motion along different possible TICT coordinates when it absorbs light. [2] K. Okuyama, Y. Numata, S. Odawara, and I. Suzuka, J. Chem. Phys., 109, 7185 (1998) and references therein. [3] A. E. Nikolaev, G. Myszkiewwicz, G. Berden, L. Meerts, J. F. Pfanstiel, and D. W. Pratt, J. Chem. Phys., 122, 084309 (2005).
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Rotationally resolved fluorescence excitation spectra of the 0(0)(0) bands of the S1<--S0 electronic transitions of 2- and 5-methylpyrimidine (2MP and 5MP, respectively) have been observed and assigned. Both spectra were found to... more
Rotationally resolved fluorescence excitation spectra of the 0(0)(0) bands of the S1<--S0 electronic transitions of 2- and 5-methylpyrimidine (2MP and 5MP, respectively) have been observed and assigned. Both spectra were found to contain two sets of rotational lines, one associated with the sigma=0 torsional level and the other associated with the sigma=+/-1 torsional level of the attached methyl group. Analyses of their structure using the appropriate torsion-rotation Hamiltonian yields the methyl group torsional barriers of V6''=1.56 and V6'=8.28 cm(-1) in 2MP and V6''=4.11 and V6'=58.88 cm(-1) in 5MP. Many of the lines in both spectra are fragmented by couplings with lower lying triplet states. Analyses of some of these perturbations yield approximate values of the intersystem crossing matrix elements, from which it is concluded that the sigma=+/-1 torsional levels of the S1 state are significantly more strongly coupled to the T1 state than the sigma=0 ...
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Rotationally resolved fluorescence excitation spectroscopy has been used to study the dynamics, electronic distribution, and the relative orientation of the transition moment vector in several vibronic transitions of acenaphthene (ACN)... more
Rotationally resolved fluorescence excitation spectroscopy has been used to study the dynamics, electronic distribution, and the relative orientation of the transition moment vector in several vibronic transitions of acenaphthene (ACN) and in its Ar van der Waals (vdW) complex. The 0(0)(0) band of the S(1) ← S(0) transition of ACN exhibits a transition moment orientation parallel to its a-inertial axis. However, some of the vibronic bands exhibit a transition moment orientation parallel to the b-inertial axis, suggesting a Herzberg-Teller coupling with the S(2) state. Additionally, some other vibronic bands exhibit anomalous intensity patterns in several of their rotational transitions. A Fermi resonance involving two near degenerate vibrations has been proposed to explain this behavior. The high-resolution electronic spectrum of the ACN-Ar vdW complex has also been obtained and fully analyzed. The results indicate that the weakly attached argon atom is located on top of the plane o...
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Rotationally resolved fluorescence excitation spectra of several torsional bands in the S1 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;-- S0 electronic spectra of 2-methylanisole (2MA) and 3-methylanisole (3MA) have been... more
Rotationally resolved fluorescence excitation spectra of several torsional bands in the S1 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;-- S0 electronic spectra of 2-methylanisole (2MA) and 3-methylanisole (3MA) have been recorded in the collision-free environment of a molecular beam. Some of the bands can be fit with rigid rotor Hamiltonians; others exhibit perturbations produced by the coupling between the internal rotation of the methyl group and the overall rotation of the entire molecule. Analyses of these data show that 2MA and 3MA both have planar heavy-atom structures; 2MA has trans-disposed methyl and methoxy groups, whereas 3MA has both cis- and trans-disposed substituents. The preferred orientations (staggered or eclipsed) in two of the conformers and the internal rotation barriers of the methyl groups in all three conformers change when they are excited by light. Additionally, the values of the barriers opposing their motion depend on the relative positions of the substituent groups, in both electronic states. In contrast, no torsional motions of the attached methoxy groups were detected. Possible reasons for these behaviors are discussed.
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The fluorescence lifetime of the zero point vibrational level of the first excited electronic state of dibenzothiophene (DBT) has been determined to be 1.0 ns by analysis of its rotationally resolved S1... more
The fluorescence lifetime of the zero point vibrational level of the first excited electronic state of dibenzothiophene (DBT) has been determined to be 1.0 ns by analysis of its rotationally resolved S1 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;-- S0 fluorescence excitation spectrum. The S1 lifetime of DBT is substantially shorter than those observed for fluorene (FLU), carbazole (CAR), and dibenzofuran (DBF), analogs of DBT in which the heavy sulfur atom is replaced by lighter ones. The electronic origin bands through the series CAR, FLU, DBF, and DBT exhibit a monotonic increase in Lorentzian broadening in their Voigt line shape profiles. Two other heterocyclic molecules manifest similar photophysical properties; 2,5-diphenylfuran and 2,5-diphenyl-1,3,4-oxadiazole. Lorentzian line shape broadenings of approximately 76 MHz were observed in the high-resolution spectra of their origin bands. Possible reasons for the short fluorescence lifetimes of these heterocycles are discussed.
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High resolution electronic spectra of 2-phenylindole (PI) and N-phenylcarbazole (PC) have been recorded in the collision-free environment of a molecular beam. Inertial defects determined from fits of the spectra were used to determine the... more
High resolution electronic spectra of 2-phenylindole (PI) and N-phenylcarbazole (PC) have been recorded in the collision-free environment of a molecular beam. Inertial defects determined from fits of the spectra were used to determine the twist angles between the two chromophores and their attached benzene rings in the ground (S0) and excited (S1) electronic states. PI was found to be significantly more planar than PC, especially in the S1 state. Stark-effect measurements of the permanent electric dipole moments of both molecules in both states show that significantly more charge is transferred from the phenyl group to the chromophore in PI (0.13e) than in PC (0.076e) when the photon is absorbed. Thereby demonstrated for the first time is a direct connection between photo-induced geometry change and charge transfer on excitation of an isolated molecule by light.
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... Yoshihara, T.; Druzhinin, SI; Demeter, A.; Kocher, N.; Stalke, D.; Zachariasse, KAKinetics of Intramolecular Charge Transfer with N-Phenylpyrrole in ... Steven T. Shipman, Justin L. Neill, Richard D. Suenram, Matt T. Muckle, and... more
... Yoshihara, T.; Druzhinin, SI; Demeter, A.; Kocher, N.; Stalke, D.; Zachariasse, KAKinetics of Intramolecular Charge Transfer with N-Phenylpyrrole in ... Steven T. Shipman, Justin L. Neill, Richard D. Suenram, Matt T. Muckle, and Brooks H. Pate. The Journal of Physical Chemistry ...
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The design of a chirped-pulse Fourier transform microwave spectrometer operating in the 2–8GHz frequency range is presented. The linear frequency sweep is generated by an arbitrary waveform generator with a sampling rate of 20 GS/s. After... more
The design of a chirped-pulse Fourier transform microwave spectrometer operating in the 2–8GHz frequency range is presented. The linear frequency sweep is generated by an arbitrary waveform generator with a sampling rate of 20 GS/s. After amplification, the microwave pulse is broadcast into a vacuum chamber where it interacts with a supersonically expanded molecular sample. The resulting molecular free induction
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ABSTRACT It is well established that biological processes involving chiral molecules can show a preference of one enantiomer relative to the other. Reported here are high resolution spectroscopy experiments that allow one to distinguish... more
ABSTRACT It is well established that biological processes involving chiral molecules can show a preference of one enantiomer relative to the other. Reported here are high resolution spectroscopy experiments that allow one to distinguish one diastereomer from another, and thereby establish if the structural requirments for diastereoism are present.
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ABSTRACT Many biochemical processes are stereospecific. An example is the physiological response to a drug that depends on its enantiomeric form. Naproxen is a drug which shows this stereo-specific physiological response. To better... more
ABSTRACT Many biochemical processes are stereospecific. An example is the physiological response to a drug that depends on its enantiomeric form. Naproxen is a drug which shows this stereo-specific physiological response. To better understand the stereo specificity of chiral substances, we observed the S_1
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Comparison of 2,3-Dibenzofuran and 1,3-Benzodioxole Using Rotationally Resolved Electronic Spectroscopy in the Gas Phase. Jessica A. Thomas, Leonardo Alvarez-Valtierra, and David W. Pratt. University of Pittsburgh. Introduction. ...
Electronic communication between donor-acceptor systems is prevalent in many chemical processes. Unfortunately, an accurate description of the changes in molecular geometry responsible for intramolecular charge transfer (ICT) is difficult... more
Electronic communication between donor-acceptor systems is prevalent in many chemical processes. Unfortunately, an accurate description of the changes in molecular geometry responsible for intramolecular charge transfer (ICT) is difficult to ascertain. Reported here are the S 0 , ...
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Gas phase rotationally resolved electronic spectra were collected for the origin and several vibronic transitions of 1,3- benzodioxole. For each band, an autocorrelation program identified the presence of two overlapping spectra which... more
Gas phase rotationally resolved electronic spectra were collected for the origin and several vibronic transitions of 1,3- benzodioxole. For each band, an autocorrelation program identified the presence of two overlapping spectra which were each fit using a least-squares algorithm to determine the rotational constants. Interpretation of these constants and how they change from one band to the next gives information