Theoretical study of the mechanism for spin‐forbidden quenching process O(¹D) + CO₂(¹Σ) → O(³P) + CO₂(¹Σ)

Abstract

ABSTRACT:The mechanism of the spin-forbidden quenching process O(was investigated by ab initio quantum chemistry methods. The calculations showed the singlet potential surface [O( 1 D)ϩCO 2 ] is attractive where a strongly bound intermediate complex CO 3 is formed in the potential basin without a transition state, whereas the complex CO 3 that is formed on the triplet surface [O( 3 P)ϩCO 3 ] must overcome a barrier. The complex channel was documented by searching minimum energy intersection points in the region of the bound complex CO 3 and calculating spin-orbit coupling at the point. A direct channel was proposed by a study of cross point of singlet and triplet PESs with different collision angles and calculations of spin-orbit coupling at those cross points in a nonbound region of the [O( 1 D)ϩCO 3 ] system. The mechanism of the energy transfer is discussed on the basis of the theoretical results.

Distribution of Vibrational States of CO2 in the Reaction O(1D) + CO2 from Time-Resolved Fourier Transform Infrared Emission Spectra

“…Carbon trioxide CO 3 was identified in solid CO 2 and Ar matrix at low temperatures with IR absorption spectroscopy; the C 2 v bridged structure was deduced to be more stable than the D 3 h symmetric structure because only the former was observed. ,,− A theoretical calculation of the system O( 1 D) + CO 2 supported this result . Calculations at various levels indicated that the energy difference between these two structures of CO 3 is within 1 kJ mol −1 , with a barrier of ∼18 kJ mol −1 from the most stable C 2 v structure for interconversion. ,, …”

“…26 Yang et al proposed that quenching of O( 1 D) by CO 2 occurs through a complex CO 3 as well as a direct collision process. 25 Here we present observations of the time-resolved IR emission spectra of product CO 2 from the quenching reaction of O( 1 D) by CO 2 . We found satisfactory agreement between observed emission spectra of CO 2 and those simulated based on a vibrational distribution of CO 2 predicted with a statistical theory.…”

“…The formation of a CO 3 complex was supported by Mebel et al, who employed multireference configuration interaction calculations to characterize the potential energy and applied statistical theories to derive rate coefficients of various channels including the intersystem singlet−triplet interactions . Yang et al proposed that quenching of O( 1 D) by CO 2 occurs through a complex CO 3 as well as a direct collision process …”

“…24 Calculations at various levels indicated that the energy difference between these two structures of CO 3 is within 1 kJ mol -1 , with a barrier of ∼18 kJ mol -1 from the most stable C 2V structure for interconversion. 9,25,26 To derive the nascent translational energies of O atoms, Matsumi et al 27 measured the Doppler profiles of O( 3 P J ), with J ) 0, 1, 2, as a function of delay between pump and probe laser pulses. O( 1 D) was produced on photolysis of N 2 O at 193 nm, and O( 3 P J ) was observed with VUV laser-induced fluorescence.…”