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Full-Text Articles in Physical Chemistry
Reactive Quenching Of Od A (2)Σ(+) By H-2: Translational Energy Distributions For H- And D-Atom Product Channels, J. H. Lehman, Jesse Lyle Bertrand , '11, Thomas Alex Stephenson, M. I. Lester
Reactive Quenching Of Od A (2)Σ(+) By H-2: Translational Energy Distributions For H- And D-Atom Product Channels, J. H. Lehman, Jesse Lyle Bertrand , '11, Thomas Alex Stephenson, M. I. Lester
Chemistry & Biochemistry Faculty Works
The H- and D-atom products from collisional quenching of OD A (2)Sigma(+) by H-2 are characterized through Doppler spectroscopy using two-photon (2 S-2 <-<- 1 S-2) laser-induced fluorescence. Partial deuteration enables separation of the channel forming H + HOD products, which accounts for 75% of reactive quenching events, from the D + H2O product channel. The Doppler profiles, along with those reported previously for other isotopic variants, are transformed into product translational energy distributions using a robust fitting procedure based on discrete velocity basis functions. The product translational energy distribution for the H- atom channel is strongly peaked at low energy (below 0.5 eV) with a long tail extending to the energetic limit. By contrast, the D-atom channel exhibits a small peak at low translational energy with a distinctive secondary peak at higher translational energy (approximately 1.8 eV) before falling off to higher energy. In both cases, most of the available energy flows into internal excitation of the water products. Similar distributions are obtained upon reanalysis of D- and H- atom Doppler profiles, respectively, from reactive quenching of OH A (2)Sigma(+) by D-2. The sum of the translational energy distributions for H- and D- atom channels is remarkably similar to that obtained for OH A (2)Sigma(+) + H-2, where the two channels cannot be distinguished from one another. The product translational energy distributions from reactive quenching are compared with those obtained from a previous experiment performed at higher collision energy, quasiclassical trajectory calculations of the post-quenching dynamics, and a statistical model. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3644763]
Experimental Characterization Of The Weakly Anisotropic Cn X(2)Σ(+) + Ne Potential From Ir-Uv Double Resonance Studies Of The Cn-Ne Complex, J. M. Beames, B. A. O'Donnell, M. Ting, M. I. Lester, Thomas Alex Stephenson
Experimental Characterization Of The Weakly Anisotropic Cn X(2)Σ(+) + Ne Potential From Ir-Uv Double Resonance Studies Of The Cn-Ne Complex, J. M. Beames, B. A. O'Donnell, M. Ting, M. I. Lester, Thomas Alex Stephenson
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IR-UV double resonance spectroscopy has been used to characterize hindered internal rotor states (n(K) = 0(0), 1(1), and 1(0)) of the CN-Ne complex in its ground electronic state with various degrees of CN stretch (nu(CN)) excitation. Rotationally resolved infrared overtone spectra of the CN-Ne complex exhibit perturbations arising from Coriolis coupling between the closely spaced hindered rotor states (1(1) and 1(0)) with two quanta of CN stretch (nu(CN) = 2). A deperturbation analysis is used to obtain accurate rotational constants and associated average CN center-of-mass to Ne separation distances as well as the coupling strength. The energetic ordering and spacings …
Theoretical And Experimental Studies Of Collision-Induced Electronic Energy Transfer From V=0-3 Of The E(0g+) Ion-Pair State Of Br2: Collisions With He And Ar, J. M. Hutchison, Robin R. O'Hern, Thomas Alex Stephenson, Y. V. Suleimanov, A. A. Buchachenko
Theoretical And Experimental Studies Of Collision-Induced Electronic Energy Transfer From V=0-3 Of The E(0g+) Ion-Pair State Of Br2: Collisions With He And Ar, J. M. Hutchison, Robin R. O'Hern, Thomas Alex Stephenson, Y. V. Suleimanov, A. A. Buchachenko
Chemistry & Biochemistry Faculty Works
Collisions of Br(2), prepared in the E(0(g)(+)) ion-pair (IP) electronic state, with He or Ar result in electronic energy transfer to the D, D('), and beta IP states. These events have been examined in experimental and theoretical investigations. Experimentally, analysis of the wavelength resolved emission spectra reveals the distribution of population in the vibrational levels of the final electronic states and the relative efficiencies of He and Ar collisions in promoting a specific electronic energy transfer channel. Theoretically, semiempirical rare gas-Br(2) potential energy surfaces and diabatic couplings are used in quantum scattering calculations of the state-to-state rate constants for electronic …
Rovibrational Resonance Effects In Collision-Induced Electronic Energy Transfer: I2(E,V=0-2)+Cf4, J. M. Hutchison, Benjamin Robert Booth Carlisle , '05, Thomas Alex Stephenson
Rovibrational Resonance Effects In Collision-Induced Electronic Energy Transfer: I2(E,V=0-2)+Cf4, J. M. Hutchison, Benjamin Robert Booth Carlisle , '05, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
Collisions of I-2 in the E(0(g)(+)) electronic state with CF4 molecules induce electronic energy transfer to the nearby D, beta, and D-' ion-pair states. Simulations of dispersed fluorescence spectra reveal collision-induced electronic energy transfer rate constants and final vibrational state distributions within each final electronic state. In comparison with earlier reports on I-2(upsilon(E)=0-2) collisions with He or Ar atoms, we find markedly different dynamics when I-2, excited to the same rovibronic states, collides with CF4. Final vibrational state distributions agree with the associated Franck-Condon factors with the initially prepared state to a greater degree than those found with He or …
Second Oh Overtone Excitation And Statistical Dissociation Dynamics Of Peroxynitrous Acid, I. M. Konen, E. X.J. Li, Thomas Alex Stephenson, M. I. Lester
Second Oh Overtone Excitation And Statistical Dissociation Dynamics Of Peroxynitrous Acid, I. M. Konen, E. X.J. Li, Thomas Alex Stephenson, M. I. Lester
Chemistry & Biochemistry Faculty Works
The second OH overtone transition of the trans-perp conformer of peroxynitrous acid (tp-HOONO) is identified using infrared action spectroscopy. HOONO is produced by the recombination of photolytically generated OH and NO(2) radicals, and then cooled in a pulsed supersonic expansion. The second overtone transition is assigned to tp-HOONO based on its vibrational frequency (10 195.3 cm(-1)) and rotational band contour, which are in accord with theoretical predictions and previous observations of the first overtone transition. The transition dipole moment associated with the overtone transition is rotated considerably from the OH bond axis, as evident from its hybrid band composition, indicating …
Response To "Kinetic And Mechanistic Studies Of The Recombination Of Oh With No2: Vibrational Deactivation, Isotopic Scrambling And Product Isomer Branching Ratios", J. Stutz, A. R. Ravishankara, J. A. Pyle, A. Tuck, M. J. Evans, H. Herrmann, M. P. Chipperfield, R. Zellner, H. Roscoe, D. E. Shallcross, R. A. Cox, P. S. Monks, S. R. Arnold, D. S. Stevenson, D. E. Heard, J. J. Remedios, R. P. Wayne, E. A. Cohen, T. Brauers, A. J. Orr-Ewing, M. A. Blitz, L. Wang, G. Duxbury, T. Dibble, C. A. Taatjes, W. Eisfeld, P. W. Seakins, A. Kovács, S. Dóbé, E. Farkas, T. Ingham, D. Rowley, C. E. Kolb, Thomas Alex Stephenson, A. J. Hynes, N. M. Donahue, I. W. M. Smith, D. Self, D. J. Donaldson
Response To "Kinetic And Mechanistic Studies Of The Recombination Of Oh With No2: Vibrational Deactivation, Isotopic Scrambling And Product Isomer Branching Ratios", J. Stutz, A. R. Ravishankara, J. A. Pyle, A. Tuck, M. J. Evans, H. Herrmann, M. P. Chipperfield, R. Zellner, H. Roscoe, D. E. Shallcross, R. A. Cox, P. S. Monks, S. R. Arnold, D. S. Stevenson, D. E. Heard, J. J. Remedios, R. P. Wayne, E. A. Cohen, T. Brauers, A. J. Orr-Ewing, M. A. Blitz, L. Wang, G. Duxbury, T. Dibble, C. A. Taatjes, W. Eisfeld, P. W. Seakins, A. Kovács, S. Dóbé, E. Farkas, T. Ingham, D. Rowley, C. E. Kolb, Thomas Alex Stephenson, A. J. Hynes, N. M. Donahue, I. W. M. Smith, D. Self, D. J. Donaldson
Chemistry & Biochemistry Faculty Works
No abstract provided.
Franck-Condon Effects In Collision-Induced Electronic Energy Transfer: I2(E;V=1,2)+He,Ar, Pooja P. Chandra , '03, Thomas Alex Stephenson
Franck-Condon Effects In Collision-Induced Electronic Energy Transfer: I2(E;V=1,2)+He,Ar, Pooja P. Chandra , '03, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
Collisions of I-2 in the E electronic state with rare gas atoms result in electronic energy transfer to the D, beta, and D-' ion-pair electronic states. Rate constants for each of these channels have been measured when I-2 is initially prepared in the J=55, v=1 and 2 levels in the E state. The rate constants and effective hard sphere collision cross sections confirm the trends observed when v=0 in the E state is initially prepared: He collisions favor population of the D state, while Ar collisions favor population of the beta state. Final state vibrational level distributions are determined by …
Collision-Induced Non-Adiabatic Transitions Between The Ion-Pair States Of Molecular Iodine: A Challenge For Experiment And Theory, T. V. Tscherbul, A. A. Buchachenko, M. E. Akopyan, S. A. Poretsky, A. M. Pravilov, Thomas Alex Stephenson
Collision-Induced Non-Adiabatic Transitions Between The Ion-Pair States Of Molecular Iodine: A Challenge For Experiment And Theory, T. V. Tscherbul, A. A. Buchachenko, M. E. Akopyan, S. A. Poretsky, A. M. Pravilov, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
The ion-pair states of molecular iodine provide a unique system for studying the efficiency, selectivity, and mechanisms of collision-induced non-adiabatic transitions. Non-adiabatic transitions between the first-tier ion-pair states in collisions with molecular partners and rare gases are analyzed and discussed. The qualitative features of the rate constants and product state distributions under single collision conditions are summarized and interpreted in terms of appropriate theoretical approaches. Two mechanisms for the non-adiabatic transitions are clearly identified. The first, operative for collisions involving molecular partners possessing permanent or transition electrostatic moments, is highly selective. It connects the initially prepared level in the E …
C-Cl Bond Fission, Hcl Elimination, And Secondary Radical Decomposition In The 193 Nm Photodissociation Of Allyl Chloride, M. L. Morton, L. J. Butler, Thomas Alex Stephenson, F. Qi
C-Cl Bond Fission, Hcl Elimination, And Secondary Radical Decomposition In The 193 Nm Photodissociation Of Allyl Chloride, M. L. Morton, L. J. Butler, Thomas Alex Stephenson, F. Qi
Chemistry & Biochemistry Faculty Works
The primary photodissociation dynamics of allyl chloride upon excitation at 193 nm is investigated in a crossed laser-molecular beam scattering apparatus. Tunable vacuum ultraviolet (VUV) photoionization of the products provides a unique ability to learn about the secondary reaction products of the nascent photoproducts formed. The data show evidence for four significant primary reaction channels: a previously unidentified low kinetic energy C-Cl bond fission channel producing unstable allyl radicals, an excited state C-Cl bond fission channel producing Cl atoms with high translational energy, an HCl elimination pathway releasing significant energy to product translation to HCl and its momentum-matched mass 40 …
Collision-Induced Electronic Energy Transfer From V=0 Of The E(0+G) Ion-Pair State In I2: Collisions With He And Ar, Christopher J. Fecko , '98, Miriam Arak Freedman , '00, Thomas Alex Stephenson
Collision-Induced Electronic Energy Transfer From V=0 Of The E(0+G) Ion-Pair State In I2: Collisions With He And Ar, Christopher J. Fecko , '98, Miriam Arak Freedman , '00, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
The electronic energy transfer pathways that occur following collisions between I-2 in the E ion-pair electronic state (v = 0, J = 55) and He and Ar atoms have been determined. The nearby D, D', and beta ion-pair states are populated, but with relative branching ratios that vary with the rare gas collision partner. In He/I-2 collisions, the D state is preferentially populated, while Ar/I-2 collisions preferentially populate the beta electronic state. Bimolecular rate constants and effective hard sphere collision cross sections have been determined for each channel; the cross sections range from 7.0 +/- 1.0 Angstrom(2) for populating the …
Collision-Induced Electronic Energy Transfer From V=0 Of The E(0g+) Ion-Pair State In I2: Collisions With I2(X), Christopher J. Fecko , '98, Miriam Arak Freedman , '00, Thomas Alex Stephenson
Collision-Induced Electronic Energy Transfer From V=0 Of The E(0g+) Ion-Pair State In I2: Collisions With I2(X), Christopher J. Fecko , '98, Miriam Arak Freedman , '00, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
The collision-induced electronic energy transfer that occurs when I-2 in the E(0(g)(+)) ion-pair electronic state collides with ground electronic state I-2 has been investigated. We prepare I-2 in single rotational levels in v = 0 of the E state using two-color double resonance laser excitation. The resulting emission spectrum shows that the nearby (DeltaT(e) = -385 cm(-1)) D(0(u)(+)) electronic state is populated. The cross section for collision-induced E -->D energy transfer is found to be IS - 3 Angstrom (2). A range of D state vibrational levels are populated, consistent with a model in which overlap between the initial …
Quantum Calculations On The Vibrational Predissociation Of Nebr2: Evidence For Continuum Resonances, Thomas Alex Stephenson, N. Halberstadt
Quantum Calculations On The Vibrational Predissociation Of Nebr2: Evidence For Continuum Resonances, Thomas Alex Stephenson, N. Halberstadt
Chemistry & Biochemistry Faculty Works
Quantum mechanical calculations on the vibrational predissociation dynamics of NeBr2 in the B electronic state have been performed and the results compared with both experimental data and other computational studies. For vibrational levels with v less than or equal to 20 we find that the vibrational state dependence of the predissociation lifetimes is in qualitative agreement with experimental measurements, as are the calculated Br-2 fragment rotational distributions. For higher vibrational levels, the B <-- X excitation profiles are well represented by a sum of two Lorentzian line shapes. We attribute this result to the presence of long-lived resonances in the dissociative continuum that are reminiscent of long-lived dissociative trajectories in previous classical studies of NeBr2. (C) 2000 American Institute of Physics. [S0021-9606(00)00205-1].
Fragment Rotational Distributions From The Dissociation Of Nebr2: Experimental And Classical Trajectory Studies, Mehdi Nejad-Sattari , '95, Thomas Alex Stephenson
Fragment Rotational Distributions From The Dissociation Of Nebr2: Experimental And Classical Trajectory Studies, Mehdi Nejad-Sattari , '95, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
The Br-2 fragment rotational distributions that result from the vibrational predissociation of NeBr2 in the B electronic state have been measured for several initial vibrational levels. In each case, the rotational distributions extend to the effective energetic Limit determined by the amount of energy available (E(av1)) for disposal into the fragment rotational and translational degrees of freedom. Analysis of the data allows refinement of the NeBr2 dissociation energy; we find that D-0=70.0 +/- 1.1 cm(-1) for the X electronic state, v = 0. Both Delta v = - 1 and -2 dissociation events have been examined. For dissociation pathways with …
Fragment Rotational State Distributions From The Dissociation Of Neibr: Experimental And Theoretical Results, Thomas Alex Stephenson
Fragment Rotational State Distributions From The Dissociation Of Neibr: Experimental And Theoretical Results, Thomas Alex Stephenson
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The IBr fragment rotational state distributions that result when the NeIBr van der Waals molecule undergoes vibrational predissociation have been measured in a pump-probe laser-induced fluorescence experiment. Independent of initial vibrational state and the number of quanta of vibrational energy lost from the I-Br coordinate, the rotational distributions extend over the full range of energetically accessible states. From the observation of energetic constraints on the rotational distribution, the dissociation energy (D0) is calculated to be 65.5 +/- 1.2 cm-1 for the A electronic state, v=16. For the X electronic state, v=0, D0=71.8 +/- 1.2 cm-1. Quantum mechanical bound state calculations …
Vibrational Branching Ratios From The Dissociation Of The Neibr Van Der Waals Molecule, Sarah Anne Walter , '91, Thomas Alex Stephenson
Vibrational Branching Ratios From The Dissociation Of The Neibr Van Der Waals Molecule, Sarah Anne Walter , '91, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
The degree of vibrational excitation in the IBr fragment from the vibrational predissociation of NeIBr (A (3)PI(1)) has been measured using two-color pump-probe laser-induced fluorescence spectroscopy. We find that for the lowest initial vibrational states examined, DELTA-upsilon = -1 dissociation pathways dominate the dynamics, while this channel is closed for upsilon greater-than-or-equal-to 17. From this result, the A state binding energy (D0) of the complex is determined to be 67 +/- 4 cm-1, while that in the X electronic state is found to be 73 +/- 4 cm-1. The X state binding energy is identical to that for NeI2 and …
Nonadiabatic Electronic Interactions In The Ion-Pair States Of Nelcl, Thomas Alex Stephenson, Y. Hong, M. I. Lester
Nonadiabatic Electronic Interactions In The Ion-Pair States Of Nelcl, Thomas Alex Stephenson, Y. Hong, M. I. Lester
Chemistry & Biochemistry Faculty Works
Nonadiabatic interactions in the NeIC1 van der Waals complex have been explored in the lowest energy triad of IC1 ion-pair states (approximately 39 000 cm-1). Dispersed fluorescence measurements reveal emission characteristic of multiple ion-pair electronic states, with the relative contributions from the E(O+ ), beta(1), and D'(2) states changing with the initial IC1 vibrational excitation (v(IC1)). Emission directly from NeIC1 (v(IC1) = O) complexes indicates that the initially prepared NeIC1 levels have mixed electronic character and that the IC1 electronic parentage changes with the initial van der Waals vibrational level selected. NeIC1 complexes prepared with 1-4 quanta of IC1 stretch …
The Spectroscopy And A State Dynamics Of The Neibr Van Der Waals Complex, William Robert Simpson , '88, Thomas Alex Stephenson
The Spectroscopy And A State Dynamics Of The Neibr Van Der Waals Complex, William Robert Simpson , '88, Thomas Alex Stephenson
Chemistry & Biochemistry Faculty Works
The A 3Π1←X 1Σ+ laser‐induced fluorescence excitation spectrum of the NeIBr van der Waals complex is reported and analyzed to extract information regarding the structure and vibrational predissociation dynamics of the complex. While no definitive geometric information regarding NeIBr is obtained, our data indicate that a linear geometry is at least plausible. The vibrational predissociation lifetimes are a strong function of A state vibrational level and range from 2.6 to 23 ps. The variation in lifetime with vibrational level is consistent with the results of previous measurements on rare gas–halogen complexes, particularly NeBr2.