Temperature-jump and trajectory studies of the quenching of CO2(010) by atomic oxygen

Abstract

A new variant of the temperature-jump method has been used to measure the rate of quenching of CO2(O10) by O(,P). The value found for the rate constant at room temperature is 1.2 & 0.2 x lo-'' cm3 molecule-' s-', in good agreement with a previous laboratory study. Our trajectory calculations show that such a large value of the room-temperature rate constant is not explicable in terms of an impulsive (Landau-Teller) mechanism but can be understood in terms of a curve-crossing (Nikitin) mechanism. However, the impulsive mechanism is still required to account for the strong temperature dependence of previous high-temperature, shock-tube results.Preliminary measurements of the rate of quenching of N,O(OlO) by O(3P) give a rate constant value similar to that found for CO,, which implies that formation of a bound triplet state of CO, plays very little part in the quenching process for CO2(O10).

Vibrational relaxation of CO2(ν2) by O(3P) in the 142–490 K temperature range

“…Previously our group measured a room temperature value of k O ( ν 2 ) of 1.8 (±0.3) × 10 −12 cm 3 s −1 in an experiment similar to that presented here [ Castle et al , 2006]. Several other studies of room temperature CO 2 ( ν 2 )‐O vibrational relaxation have been published [ Khvorostovskaya et al , 2002; Pollock et al , 1993; Scott et al , 1993; Shved et al , 1991] with room temperature laboratory measurements of k O ( ν 2 ) clustered in the 1.2–1.8 × 10 −12 cm 3 s −1 range. Interestingly, there is a marked discrepancy between the experimental values of k O ( ν 2 ) and those obtained through analysis of field data.…”

Vibrational relaxation of CO2(ν2) by atomic oxygen

“…Phillips and coworkers [ Pollock et al , 1993; Scott et al , 1993] analyzed the approach to equilibrium of the CO 2 [01 1 0] population following ultraviolet flash photolysis of Ar‐O 3 ‐CO 2 mixtures, using the temperature‐jump method. The O 3 photolysis produced O atoms and also served to heat the mixture by approximately 12 K, giving rise to a slightly enhanced steady state CO 2 [01 1 0] population.…”

Vibrational quenching of CO2(010) by collisions with O(P3) at thermal energies: A quantum-mechanical study

“…A similar situation occurs for the other symmetry blocks, which involve fragments with j = 1 and 2, and where avoided crossings with states correlating with vibrationally relaxed CO 2 only occur for states correlating with CO 2 ͑010͒ and j = 2. This type of mechanism was early proposed by Nikitin and Umansky 13 for collisions involving open-shell atoms or molecules and later postulated by Scott et al 12 to explain the large value of the relaxation rate of CO 2 ͑010͒ + O observed at room temperature. Moreover, we have found that, for the initial state j = 2 and low collision energies, the largest populations are obtained for products with j = 0 and 1.…”

“…The most recent theoretical study for this process was carried out by Scott et al, 12 assuming a perpendicular approach of the colliding particle and performing quasiclassical trajectory calculations on an adjustable Morse-type CO 2 -O interaction potential. This single-surface approach was capable of describing the high-temperature dependence of k. To reproduce the low-temperature dependence of the relaxation rate constant, however, Scott et al resorted to a curve-crossing model proposed by Nikitin and Umanski 13 for VET processes involving open-shell species.…”