Temperature dependence of the photodissociation of CO₂ from high vibrational levels: 205-230 nm imaging studies of CO(X¹Σ⁺) and O(³P, ¹D) products

Journal Article · Thu Apr 20 00:00:00 EDT 2017 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4979952· OSTI ID:1465971

Sutradhar, S.  ^[1]; Samanta, B. R. ^[1]; Samanta, A. K. ^[1]; Reisler, H.  ^[1]

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1. Univ. of Southern California, Los Angeles, CA (United States). Dept. of Chemistry

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.

• Research Organization: Univ. of Southern California, Los Angeles, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: FG02-05ER15629
• OSTI ID: 1465971
• Alternate ID(s): OSTI ID: 1361815
• Journal Information: Journal of Chemical Physics, Vol. 147, Issue 1; ISSN 0021-9606
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

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