| The role of vibrations in the atmosphere has been explored in two cases.;A new mechanism for OH production in the mesosphere is assessed. Vibrationally excited H2, formed by the collisional energy transfer from O2S+ g1 , reacts with O(3P) to yield OH. This contributes 16% to the total OH production at 100 km altitude.;Overtone-induced chemistry of trifluoroacetic acid is considered. The elimination of HF is the lowest energy dissociation pathway [50.3 kcal mol −1 (MP2/6-311G(2d,p))]. The second fragment forms a stable fluorinated epoxide, CF2CO2. The absorption cross sections of the vOH = 3, 4, 5 overtones are (2.70 ± 0.09) × 10−20, (1.68 ± 0.19) × 10−21 , and ∼1.5 × 10−22 cm2 molec−1 cm−1, respectively. Excitation to the vOH = 5 or 6 leads to dissociation; the rate constants are 3.7 × 10−9 and 2.5 × 10 −10 s−1, respectively. The overtone-driven photodissociation is more important than the ultraviolet photodissociation in the troposphere, but is insignificant in comparison to wet deposition and reaction with OH. |
