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

Abstract

The CO 2 ͑010͒ -O͑ 3 P͒ vibrational energy transfer ͑VET͒ efficiency is a key input to aeronomical models of the energy budget of the upper atmospheres of Earth, Venus, and Mars. This work addresses the physical mechanisms responsible for the high efficiency of the VET process at the thermal energies existing in the terrestrial upper atmosphere ͑150 K ഛ T ഛ 550 K͒. We present a quantum-mechanical study of the process within a reduced-dimensionality approach. In this model, all the particles remain along a plane and the O͑ 3 P͒ atom collides along the C 2v symmetry axis of CO 2 , which can present bending oscillations around the linear arrangement, while the stretching C-O coordinates are kept fixed at their equilibrium values. Two kinds of scattering calculations are performed on high-quality ab initio potential energy surfaces ͑PESs͒. In the first approach, the calculations are carried out separately for each one of the three PESs correlating to O͑ 3 P͒. In the second approach, nonadiabatic effects induced by spin-orbit couplings ͑SOC͒ are also accounted for. The results presented here provide an explanation to some of the questions raised by the experiments and aeronomical observations. At thermal energies, nonadiabatic transitions induced by SOC play a key role in causing large VET efficiencies, the process being highly sensitive to the initial fine-structure level of oxygen. At higher energies, the two above-mentioned approaches tend to coincide towards an impulsive Landau-Teller mechanism of the vibrational to translational ͑V-T͒ energy transfer.

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

“…In the theoretical area, de Lara‐Castells et al [2006, 2007] performed the first fully quantum calculations on the CO 2 ( ν 2 ) + O system at thermal energies using high‐quality ab initio potential energy surfaces. Their results show that at thermal temperatures the O( 3 P J = 2 ) spin sublevel dominates CO 2 ( ν 2 ) quenching due to favorable spin‐orbit couplings, and predict k O ( ν 2 ) = 1.8 × 10 −12 cm 3 s −1 at 300 K in excellent agreement with the present experiment.…”

“… De Lara‐Castells et al [2007] performed the first quantum mechanical calculations on the CO 2 ( ν 2 ) + O system at thermal energies. These quantum scattering calculations used high‐quality ab initio potential energy surfaces [ de Lara‐Castells et al , 2006] and predict a temperature dependence of k O ( ν 2 ) dependent upon the O atom fine structure. Their results show that for O( 3 P J=0,1 ) spin‐orbit states, the associated rate coefficient should be proportional to exp(T −1/3 ) (Landau‐Teller behavior) while for O( 3 P J=2 ) the rate coefficient is expected to have T 1/2 dependence.…”

CO<sub>2</sub>(ν<sub>2</sub>)-O quenching rate coefficient derived from coincidental SABER/TIMED and Fort Collins lidar observations of the mesosphere and lower thermosphere

“…As the quantum-mechanical calculations show (de Lara-Castells et al, 2006), the vibrational quenching of CO 2 (ν 2 ) is significantly enhanced by spin-orbit interaction, the probability of which depends on energy, so positive temperature dependency should be expected. In the present study we already used a standard (T /300) 1/2 temperature scaling of k VT , so one has to assume that the temperature dependency is stronger than T 1/2 .…”

Cross Sections and Reaction Rates for Comparative Planetary Aeronomy

“…3. The more recent calculations by de Lara-Castells et al (2006 of CO 2 + O( 3 P), also included a representation of spin-orbit coupling. The two independent sets of potential energy surfaces provide strong support for the concept that the O( 3 P J ) fine structure states play critical roles in CO 2 (010) excitation and relaxation, as illustrated by the reaction CO 2 (000) + O( 3 P 0,1 ) ↔ CO 2 (010) + O( 3 P 1,2 ) (33) which will be discussed further below.…”