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Title: Photodissociation dynamics of nitrobenzene and o-nitrotoluene

Abstract

Photodissociation of nitrobenzene at 193, 248, and 266 nm and o-nitrotoluene at 193 and 248 nm was investigated separately using multimass ion imaging techniques. Fragments corresponding to NO and NO{sub 2} elimination from both nitrobenzene and o-nitrotoluene were observed. The translational energy distributions for the NO elimination channel show bimodal distributions, indicating two dissociation mechanisms involved in the dissociation process. The branching ratios between NO and NO{sub 2} elimination channels were determined to be NO/NO{sub 2}=0.32{+-}0.12 (193 nm), 0.26{+-}0.12 (248 nm), and 0.4{+-}0.12(266 nm) for nitrobenzene and 0.42{+-}0.12(193 nm) and 0.3{+-}0.12 (248 nm) for o-nitrotoluene. Additional dissociation channels, O atom elimination from nitrobenzene, and OH elimination from o-nitrotoluene, were observed. New dissociation mechanisms were proposed, and the results are compared with potential energy surfaces obtained from ab initio calculations. Observed absorption bands of photodissociation are assigned by the assistance of the ab initio calculations for the relative energies of the triplet excited states and the vertical excitation energies of the singlet and triplet excited states of nitrobenzene and o-nitrotoluene. Finally, the dissociation rates and lifetimes of photodissociation of nitrobenzene and o-nitrotoluene were predicted and compared to experimental results.

Authors:
; ; ; ;  [1];  [2];  [2];  [3]
  1. Institute of Atomic and Molecular Sciences, Academia Sinica, P.O. Box 23-166, Taipei, Taiwan (China)
  2. (United States)
  3. (China)
Publication Date:
OSTI Identifier:
20991220
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 126; Journal Issue: 6; Other Information: DOI: 10.1063/1.2435351; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; BRANCHING RATIO; DISSOCIATION; ENERGY SPECTRA; EXCITED STATES; NITRIC OXIDE; NITROBENZENE; NITROGEN DIOXIDE; PHOTOLYSIS; REACTION KINETICS

Citation Formats

Lin, Ming-Fu, Lee, Yuan T., Ni, Chi-Kung, Xu, Shucheng, Lin, M. C., Department of Chemistry, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Center for Interdisciplinary Molecular Science, National Chiao Tung University, Hsinchu, Taiwan. Photodissociation dynamics of nitrobenzene and o-nitrotoluene. United States: N. p., 2007. Web. doi:10.1063/1.2435351.
Lin, Ming-Fu, Lee, Yuan T., Ni, Chi-Kung, Xu, Shucheng, Lin, M. C., Department of Chemistry, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Emory University, Atlanta, Georgia 30322, & Center for Interdisciplinary Molecular Science, National Chiao Tung University, Hsinchu, Taiwan. Photodissociation dynamics of nitrobenzene and o-nitrotoluene. United States. doi:10.1063/1.2435351.
Lin, Ming-Fu, Lee, Yuan T., Ni, Chi-Kung, Xu, Shucheng, Lin, M. C., Department of Chemistry, Emory University, Atlanta, Georgia 30322, Department of Chemistry, Emory University, Atlanta, Georgia 30322, and Center for Interdisciplinary Molecular Science, National Chiao Tung University, Hsinchu, Taiwan. Wed . "Photodissociation dynamics of nitrobenzene and o-nitrotoluene". United States. doi:10.1063/1.2435351.
@article{osti_20991220,
title = {Photodissociation dynamics of nitrobenzene and o-nitrotoluene},
author = {Lin, Ming-Fu and Lee, Yuan T. and Ni, Chi-Kung and Xu, Shucheng and Lin, M. C. and Department of Chemistry, Emory University, Atlanta, Georgia 30322 and Department of Chemistry, Emory University, Atlanta, Georgia 30322 and Center for Interdisciplinary Molecular Science, National Chiao Tung University, Hsinchu, Taiwan},
abstractNote = {Photodissociation of nitrobenzene at 193, 248, and 266 nm and o-nitrotoluene at 193 and 248 nm was investigated separately using multimass ion imaging techniques. Fragments corresponding to NO and NO{sub 2} elimination from both nitrobenzene and o-nitrotoluene were observed. The translational energy distributions for the NO elimination channel show bimodal distributions, indicating two dissociation mechanisms involved in the dissociation process. The branching ratios between NO and NO{sub 2} elimination channels were determined to be NO/NO{sub 2}=0.32{+-}0.12 (193 nm), 0.26{+-}0.12 (248 nm), and 0.4{+-}0.12(266 nm) for nitrobenzene and 0.42{+-}0.12(193 nm) and 0.3{+-}0.12 (248 nm) for o-nitrotoluene. Additional dissociation channels, O atom elimination from nitrobenzene, and OH elimination from o-nitrotoluene, were observed. New dissociation mechanisms were proposed, and the results are compared with potential energy surfaces obtained from ab initio calculations. Observed absorption bands of photodissociation are assigned by the assistance of the ab initio calculations for the relative energies of the triplet excited states and the vertical excitation energies of the singlet and triplet excited states of nitrobenzene and o-nitrotoluene. Finally, the dissociation rates and lifetimes of photodissociation of nitrobenzene and o-nitrotoluene were predicted and compared to experimental results.},
doi = {10.1063/1.2435351},
journal = {Journal of Chemical Physics},
number = 6,
volume = 126,
place = {United States},
year = {Wed Feb 14 00:00:00 EST 2007},
month = {Wed Feb 14 00:00:00 EST 2007}
}
  • Laser-powered homogeneous pyrolysis (LPHP) has been used to study the gas-phase thermal decomposition of nitrobenzene (NB), m-dinitrobenzene (m-DNB), p-nitrotoluene (p-NT), o-nitrotoluene (o-NT), and 2,4-dinitrotoluene (2,4-DNT) under conditions where surface-catalyzed reactions are precluded. The Arrhenius parameters have been determined by comparative rate measurements relative to cyclohexene decomposition and the reaction mechanisms have been established. In all cases, the rate-limiting step is the homolysis of the Ar-NO2 bond. The measured Arrhenius parameters for homolysis range from log A = 14.5 to 16.4 and E/sub a/ from 67.0 to 70.0 kcal/mol. The c-NO2 bond dissociation energies (kcal/mol) and values of log k (smore » ) for NB, m-DNB, p-NT, o-NT, and 2,4-DNT have been derived from these results and are as follows: 71.4 +/- 2.0, (15.5 +/- 0.5) - (68.2 +/- 1.7)/2.3RT; 73.2 +/- 2.4, (14.5 +/- 0.5) - (70.0 +/- 2.1)/2.3RT; 71.4 +/- 2.3, (14.9 +/- 0.5) - (68.2 +/- 2.0)/2.3RT; 70.2 +/- 2.5, (16.4 +/- 0.6) - (67.0 +/- 2.2)/2.3RT; 70.6 +/- 2.0, (15.3 +/- 0.4) - (67.4 +/- 1.7)/2.3RT. 15 references, 6 figures, 4 tables.« less
  • The photodissociation dynamics of O{sub 2}, O{sub 2} + hυ → O({sup 3}P) + O(2p{sup 3}({sup 4}S)3s, {sup 3}S/{sup 5}S), has been studied by combining the XUV laser pump / UV laser probe and velocity map imaging methods in the photon energy range 14.64–15.20 eV. The fragment yield spectra of O({sup 3}S) and O({sup 5}S) and their velocity map images have been recorded using the state-selective (1+1) REMPI method to detect the fragments. The fragment yield spectra show resolved fine structure that arises from the predissociated Rydberg states I, I{sup ′} and I{sup ″} ({sup 3}Π{sub Ω=0,1,2}). The branching ratiosmore » between the two decay channels have been measured by one-photon ionization of the fragments O({sup 3}S) and O({sup 5}S) simultaneously. It is surprising to find that the dissociation cross sections for the production of O({sup 5}S) are larger than, or comparable to, those of O({sup 3}S) for the I and I{sup ′} states, while the cross sections for the production of O({sup 5}S) are smaller than those of O({sup 3}S) for the I{sup ″} state. All fragments O({sup 5}S) arise from perpendicular transitions, which provides direct experimental evidence about the symmetry assignments of the states I, I{sup ′} and I{sup ″} excited in this energy region. Although most of the fragments O({sup 3}S) arise from perpendicular transitions, some of them are from parallel transitions. Based on the calculated ab initio potential energy curves, we propose that the neutral dissociation into O({sup 3}P) + O({sup 3}S) occurs mainly via the interaction of the Rydberg states I, I{sup ′}, and I{sup ″} with the vibrational continuum of the diabatic 8{sup 3}Π{sub u} state (1π{sub u}{sup −1}(a{sup 4}Π{sub u})3sσ{sub g},{sup 3}Π{sub u}), while the neutral dissociation into O({sup 3}P) + O({sup 5}S) occurs mainly via the interaction of Rydberg states I, I{sup ′}, and I{sup ″} with the diabatic 7{sup 3}Π{sub u} (1π{sub g}{sup −1}(X{sup 2}Π{sub g})3pσ{sub u},{sup 3}Π{sub u})« less
  • In this work, we have first employed the combined quantum mechanics/molecular mechanics (QM/MM) method to study the photodissociation mechanism of thioacetic acid CH{sub 3}C(O)SH in the S{sub 1}, T{sub 1}, and S{sub 0} states in argon matrix. CH{sub 3}C(O)SH is treated quantum mechanically using the complete active space self-consistent field and complete active space second-order perturbation theory methods; argon matrix is described classically using Lennard-Jones potentials. We find that the C-S bond fission is predominant due to its small barriers of ca. 3.0 and 1.0 kcal/mol in the S{sub 1} and T{sub 1} states. It completely suppresses the nearby C—Cmore » bond fission. After the bond fission, the S{sub 1} radical pair of CH{sub 3}CO and SH can decay to the S{sub 0} and T{sub 1} states via internal conversion and intersystem crossing, respectively. In the S{sub 0} state, the radical pair can either recombine to form CH{sub 3}C(O)SH or proceed to form molecular products of CH{sub 2}CO and H{sub 2}S. We have further employed our recently developed QM/MM generalized trajectory-based surface-hopping method to simulate the photodissociation dynamics of CH{sub 3}C(O)SH. In 1 ps dynamics simulation, 56% trajectories stay at the Franck-Condon region; the S{sub 1} C—S bond fission takes place in the remaining 44% trajectories. Among all nonadiabatic transitions, the S{sub 1} → S{sub 0} internal conversion is major (55%) but the S{sub 1} → T{sub 1} intersystem crossing is still comparable and cannot be ignored, which accounts for 28%. Finally, we have found a radical channel generating the molecular products of CH{sub 2}CO and H{sub 2}S, which is complementary to the concerted molecular channel. The present work sets the stage for simulating photodissociation dynamics of similar thio-carbonyl systems in matrix.« less
  • Oxygen Rydberg time-of-flight spectroscopy was used to study the vacuum ultraviolet photodissociation dynamics of N{sub 2}O near 130 nm. The O({sup 3}P{sub J}) products were tagged by excitation to high-n Rydberg levels and subsequently field ionized at a detector. In agreement with previous work, we find that O({sup 3}P{sub J}) formation following excitation to the repulsive N{sub 2}O D({sup 1}{sigma}{sup +}) state produces the first two electronically excited states of the N{sub 2} counterfragment, N{sub 2}(A {sup 3}{sigma}{sub u}{sup +}) and N{sub 2}(B {sup 3}{pi}{sub g}). The O({sup 3}P{sub J}) translational energy distribution reveals that the overall branching ratio betweenmore » N{sub 2}(A {sup 3}{sigma}{sub u}{sup +}) and N{sub 2}(B {sup 3}{pi}{sub g}) formation is approximately 1.0:1.0 for J=1 and 2, with slightly less N{sub 2}(B {sup 3}{pi}{sub g}) produced in coincidence with O({sup 3}P{sub 0}). The angular distributions were found to be independent of J and highly anisotropic, with {beta}=1.5{+-}0.2.« less