Nonadiabatic couplings in the collisional removal of O(2)(b (1)Sigma(g) (+),v) by O(2)

Model of Daytime Oxygen Emissions in the Mesopause Region and Above: A Review and New Results

Atmospheric emissions of atomic and molecular oxygen have been observed since the middle of 19th century. In the last decades, it has been shown that emissions of excited oxygen atom O(1D) and molecular oxygen in electronically–vibrationally excited states O2(b1Σ+g, v) and O2(a1Δg, v) are related by a unified photochemical mechanism in the mesosphere and lower thermosphere (MLT). The current paper consists of two parts: a review of studies related to the development of the model of ozone and molecular oxygen photodissociation in the daytime MLT and new results. In particular, the paper includes a detailed description of formation mechanism for excited oxygen components in the daytime MLT and presents comparison of widely used photochemical models. The paper also demonstrates new results such as new suggestions about possible products for collisional reactions of electronically–vibrationally excited oxygen molecules with atomic oxygen and new estimations of O2(b1Σ+g, v = 0–10) radiative lifetimes which are necessary for solving inverse problems in the lower thermosphere. Moreover, special attention is given to the “Barth’s mechanism” in order to demonstrate that for different sets of fitting coefficients its contribution to O2(b1Σ+g, v) and O2(a1Δg, v) population is neglectable in daytime conditions. In addition to the review and new results, possible applications of the daytime oxygen emissions are presented, e.g., the altitude profiles O(3P), O3 and CO2 can be retrieved by solving inverse photochemical problems when emissions from electronically vibrationally excited states of O2 molecule are used as proxies.

O2(b1Σg+) Quenching by O2, CO2, H2O, and N2 at Temperatures of 300-800 K

Rate constants for the removal of O₂(b¹Σ_g⁺) by collisions with O₂, N₂, CO₂, and H₂O have been determined over the temperature range from 297 to 800 K. O₂(b¹Σ_g⁺) was excited by pulses from a tunable dye laser, and the deactivation kinetics were followed by observing the temporal behavior of the b¹Σ_g⁺-X³Σ_g^- fluorescence. The removal rate constants for CO₂, N₂, and H₂O were not strongly dependent on temperature and could be represented by the expressions k_CO2 = (1.18 ± 0.05) × 10^-17 × T^1.5 × exp[Formula: see text], k_N2 = (8 ± 0.3) × 10^-20 × T^1.5 × exp[Formula: see text], and k_H2O = (1.27 ± 0.08) × 10^-16 × T^1.5 × exp[Formula: see text] cm³ molecule^-1 s^-1. Rate constants for O₂(b¹Σ_g⁺) removal by O₂(X), being orders of magnitude lower, demonstrated a sharp increase with temperature, represented by the fitted expression k_O2 = (7.4 ± 0.8) × 10^-17 × T^0.5 × exp[Formula: see text] cm³ molecule^-1 s^-1. All of the rate constants measured at room temperature were found to be in good agreement with previously reported values.

Dimol Emission of Oxygen Made Possible by Repulsive Interaction

For the energy emitted in a textbook example of chemiluminescence, the peculiar red light produced by singlet molecular oxygen is about twice that of the spin-forbidden O₂(a¹Δ_g) → O₂(X³∑_g^-) transition. Theoretical studies suggest that the O₂(a¹Δ_g)-O₂(a¹Δ_g) van der Waals interaction is weak, and at room temperature no long-lived complex is formed. Our high-level ab initio calculations show that in the bound domain of the dimer, the oscillator strength is very small, but increases at smaller intermolecular separations, where, however, the interaction is repulsive. We propose that the emission is induced by collisions: it takes place "on-the-fly", when the collision energy allows the system to access the repulsive part of the potential energy surface where the oscillator strength is relatively large. The contribution of different orientations of the two O₂ molecules to the emission has been evaluated with a simple semiclassical model. The position of the emission peak is in accord with the experiment, and the estimated rate coefficient of collision-induced emission averaged over orientation is in reasonable agreement with the measurements.