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Title: Temperature dependence of the photodissociation of CO 2 from high vibrational levels: 205-230 nm imaging studies of CO(X 1Σ +) and O( 3P, 1D) products

Abstract

In this paper, the 205-230 nm photodissociation of vibrationally excited CO 2 at temperatures up to 1800 K was studied using Resonance Enhanced Multiphoton Ionization (REMPI) and time-sliced Velocity Map Imaging (VMI). CO 2 molecules seeded in He were heated in an SiC tube attached to a pulsed valve and supersonically expanded to create a molecular beam of rotationally cooled but vibrationally hot CO 2. Photodissociation was observed from vibrationally excited CO 2 with internal energies up to about 20 000 cm -1, and CO(X 1Σ +), O( 3P), and O( 1D) products were detected by REMPI. The large enhancement in the absorption cross section with increasing CO 2 vibrational excitation made this investigation feasible. The internal energies of heated CO 2 molecules that absorbed 230 nm radiation were estimated from the kinetic energy release (KER) distributions of CO(X 1Σ +) products in v" = 0. At 230 nm, CO 2 needs to have at least 4000 cm -1 of rovibrational energy to absorb the UV radiation and produce CO(X 1Σ +) + O( 3P). CO 2 internal energies in excess of 16 000 cm -1 were confirmed by observing O( 1D) products. It is likely that initial absorption frommore » levels with high bending excitation accesses both the A 1B 2 and B 1A 2 states, explaining the nearly isotropic angular distributions of the products. CO(X 1Σ +) product internal energies were estimated from REMPI spectroscopy, and the KER distributions of the CO(X 1Σ +), O( 3P), and O( 1D) products were obtained by VMI. The CO product internal energy distributions change with increasing CO 2 temperature, suggesting that more than one dynamical pathway is involved when the internal energy of CO 2 (and the corresponding available energy) increases. The KER distributions of O( 1D) and O( 3P) show broad internal energy distributions in the CO(X 1Σ +) cofragment, extending up to the maximum allowed by energy but peaking at low KER values. Finally, although not all the observations can be explained at this time, with the aid of available theoretical studies of CO 2 VUV photodissociation and O + CO recombination, it is proposed that following UV absorption, the two lowest lying triplet states, a 3B 2 and b 3A 2, and the ground electronic state are involved in the dynamical pathways that lead to product formation.« less

Authors:
ORCiD logo [1];  [1];  [1]; ORCiD logo [1]
  1. Univ. of Southern California, Los Angeles, CA (United States). Dept. of Chemistry
Publication Date:
Research Org.:
Univ. of Southern California, Los Angeles, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1465971
Alternate Identifier(s):
OSTI ID: 1361815
Grant/Contract Number:  
FG02-05ER15629
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 147; Journal Issue: 1; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Boltzmann equations; excited states; photodissociation; carbon dioxide; atomic and molecular beams; spin orbit interactions; ground states; dissociation energies; molecular dissociation

Citation Formats

Sutradhar, S., Samanta, B. R., Samanta, A. K., and Reisler, H. Temperature dependence of the photodissociation of CO2 from high vibrational levels: 205-230 nm imaging studies of CO(X1Σ+) and O(3P, 1D) products. United States: N. p., 2017. Web. doi:10.1063/1.4979952.
Sutradhar, S., Samanta, B. R., Samanta, A. K., & Reisler, H. Temperature dependence of the photodissociation of CO2 from high vibrational levels: 205-230 nm imaging studies of CO(X1Σ+) and O(3P, 1D) products. United States. doi:10.1063/1.4979952.
Sutradhar, S., Samanta, B. R., Samanta, A. K., and Reisler, H. Thu . "Temperature dependence of the photodissociation of CO2 from high vibrational levels: 205-230 nm imaging studies of CO(X1Σ+) and O(3P, 1D) products". United States. doi:10.1063/1.4979952. https://www.osti.gov/servlets/purl/1465971.
@article{osti_1465971,
title = {Temperature dependence of the photodissociation of CO2 from high vibrational levels: 205-230 nm imaging studies of CO(X1Σ+) and O(3P, 1D) products},
author = {Sutradhar, S. and Samanta, B. R. and Samanta, A. K. and Reisler, H.},
abstractNote = {In this paper, the 205-230 nm photodissociation of vibrationally excited CO2 at temperatures up to 1800 K was studied using Resonance Enhanced Multiphoton Ionization (REMPI) and time-sliced Velocity Map Imaging (VMI). CO2 molecules seeded in He were heated in an SiC tube attached to a pulsed valve and supersonically expanded to create a molecular beam of rotationally cooled but vibrationally hot CO2. Photodissociation was observed from vibrationally excited CO2 with internal energies up to about 20 000 cm-1, and CO(X1Σ+), O(3P), and O(1D) products were detected by REMPI. The large enhancement in the absorption cross section with increasing CO2 vibrational excitation made this investigation feasible. The internal energies of heated CO2 molecules that absorbed 230 nm radiation were estimated from the kinetic energy release (KER) distributions of CO(X1Σ+) products in v" = 0. At 230 nm, CO2 needs to have at least 4000 cm-1 of rovibrational energy to absorb the UV radiation and produce CO(X1Σ+) + O(3P). CO2 internal energies in excess of 16 000 cm-1 were confirmed by observing O(1D) products. It is likely that initial absorption from levels with high bending excitation accesses both the A1B2 and B1A2 states, explaining the nearly isotropic angular distributions of the products. CO(X1Σ+) product internal energies were estimated from REMPI spectroscopy, and the KER distributions of the CO(X1Σ+), O(3P), and O(1D) products were obtained by VMI. The CO product internal energy distributions change with increasing CO2 temperature, suggesting that more than one dynamical pathway is involved when the internal energy of CO2 (and the corresponding available energy) increases. The KER distributions of O(1D) and O(3P) show broad internal energy distributions in the CO(X1Σ+) cofragment, extending up to the maximum allowed by energy but peaking at low KER values. Finally, although not all the observations can be explained at this time, with the aid of available theoretical studies of CO2 VUV photodissociation and O + CO recombination, it is proposed that following UV absorption, the two lowest lying triplet states, a3B2 and b3A2, and the ground electronic state are involved in the dynamical pathways that lead to product formation.},
doi = {10.1063/1.4979952},
journal = {Journal of Chemical Physics},
number = 1,
volume = 147,
place = {United States},
year = {Thu Apr 20 00:00:00 EDT 2017},
month = {Thu Apr 20 00:00:00 EDT 2017}
}

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