skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Nonadiabatic photodissociation dynamics in (HI){sub 2} induced by intracluster collisions

Abstract

The sequential photodissociation dynamics of (HI){sub 2} is studied by means of a nonadiabatic wave packet treatment starting from the I{sup *}-HI complex. The model reproduces the main experimental findings for photolysis with 266 nm radiation. The results confirm that some of the H atoms dissociated from the I{sup *}-HI complex deactivate the I{sup *} atom through a H/I{sup *} intracluster collision which induces an I{sup *}{yields}I electronically nonadiabatic transition. As a consequence, these H fragments become very fast by acquiring nearly all the I{sup *} excitation energy, equivalent to the I{sup *}/I spin-orbit splitting. A most interesting result is the high production of bound I{sub 2} fragments in highly excited rovibrational states in the photolysis, indicating that the H dissociation is mainly direct.

Authors:
; ;  [1]
  1. Instituto de Matematicas y Fisica Fundamental, C.S.I.C., Serrano 123, 28006 Madrid (Spain)
Publication Date:
OSTI Identifier:
20991251
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 126; Journal Issue: 16; Other Information: DOI: 10.1063/1.2731371; (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; DISSOCIATION; IODINE; IODINE IONS; L-S COUPLING; MOLECULAR CLUSTERS; PHOTOLYSIS; PHOTON-MOLECULE COLLISIONS; REACTION KINETICS; SPIN; VIBRATIONAL STATES; WAVE PACKETS

Citation Formats

Lopez-Lopez, S., Prosmiti, R., and Garcia-Vela, A. Nonadiabatic photodissociation dynamics in (HI){sub 2} induced by intracluster collisions. United States: N. p., 2007. Web. doi:10.1063/1.2731371.
Lopez-Lopez, S., Prosmiti, R., & Garcia-Vela, A. Nonadiabatic photodissociation dynamics in (HI){sub 2} induced by intracluster collisions. United States. doi:10.1063/1.2731371.
Lopez-Lopez, S., Prosmiti, R., and Garcia-Vela, A. Sat . "Nonadiabatic photodissociation dynamics in (HI){sub 2} induced by intracluster collisions". United States. doi:10.1063/1.2731371.
@article{osti_20991251,
title = {Nonadiabatic photodissociation dynamics in (HI){sub 2} induced by intracluster collisions},
author = {Lopez-Lopez, S. and Prosmiti, R. and Garcia-Vela, A.},
abstractNote = {The sequential photodissociation dynamics of (HI){sub 2} is studied by means of a nonadiabatic wave packet treatment starting from the I{sup *}-HI complex. The model reproduces the main experimental findings for photolysis with 266 nm radiation. The results confirm that some of the H atoms dissociated from the I{sup *}-HI complex deactivate the I{sup *} atom through a H/I{sup *} intracluster collision which induces an I{sup *}{yields}I electronically nonadiabatic transition. As a consequence, these H fragments become very fast by acquiring nearly all the I{sup *} excitation energy, equivalent to the I{sup *}/I spin-orbit splitting. A most interesting result is the high production of bound I{sub 2} fragments in highly excited rovibrational states in the photolysis, indicating that the H dissociation is mainly direct.},
doi = {10.1063/1.2731371},
journal = {Journal of Chemical Physics},
number = 16,
volume = 126,
place = {United States},
year = {Sat Apr 28 00:00:00 EDT 2007},
month = {Sat Apr 28 00:00:00 EDT 2007}
}
  • Photodissociation dynamics of iodoacetonitrile (ICH{sub 2}CN) have been investigated at pump wavelengths of 266 and 304 nm using a photofragment ion image velocity mapping technique. At both wavelengths, the prompt C-I bond rupture takes place on the repulsive excited states to give I({sup 2}P{sub 3/2}) and I*({sup 2}P{sub 1/2}), and their speed and spatial distributions are simultaneously measured. The recoil anisotropy parameter ({beta}) at 266 nm is determined to be 1.10 and 1.60 for I and I*, respectively, while it is found to be much higher at 304 nm to give {beta}=1.70 and 1.90 for I and I*, respectively. Themore » branching ratios for I*/I channels are measured to be 0.724 and 0.136 at 266 and 304 nm, respectively, giving insights on nonadiabatic transition phenomena and relative oscillator strengths of optically accessible transitions of ICH{sub 2}CN. Accordingly, relative oscillator strengths of parallel/perpendicular transitions and nonadiabatic transitions among the excited states are quantitatively characterized. A large portion of the available energy (41%-48%) goes into the internal energy of the CH{sub 2}CN fragment. A modified impulsive model in which the CH{sub 2}CN fragment is assumed to be rigid predicts the energy disposal quite well. Delocalization of an unpaired electron of the CH{sub 2}CN radical during the C-I bond cleavage, leading to a large structural change of the CH{sub 2}CN moiety, may be responsible for internally hot fragments.« 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
  • Photodissociation of diatomic molecules to open-shell atoms is shown to be very strongly affected by nonadiabatic interactions when the photon energy is just above the threshold for dissociation. The energy dependences of photodissociation cross sections and various anisotropy parameters exhibit a wealth of structure in conformity with their theoretical predictions that nonadiabatic interactions between molecular states, approaching the same atomic term limit, lead to the emergence of resonance features in the spectra. Some of these features are associated with Feshbach and shape resonances on states that carry no oscillator strength in zeroth order. As an example, they consider the photodissociationmore » cross sections for the production of individual C/sup +/(/sup 2/P/sub 3/2,1/2/) states from selected initial CH/sup +/ levels and the fragment angular distribution, orientation, and alignment. They discuss how totally oriented fragments can be produced by near-threshold photodissociation in a magnetic field.« less