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Vibrational relaxation of H

Vibrational relaxation of H2O(v2,v13) molecules by collisions with Ar was studied at 298 K (v2 denotes the bending vibrational mode and v13 denotes the sum of the symmetric, v1, and asymmetric, v3, vibrational modes). The H2O molecules from 14 different exothermic reactions of H-atom abstraction by OH radicals were observed by infrared emission from a fast flow reactor as a function of Ar pressure and reaction time. Numerical kinetic calculations were used to obtain rate constants for stretch-to-bend energy conversion, (v2,v13) → (v2 + 2,v13 − 1), and pure bend relaxation, (v2,v13) → (v2 − 1,v13). Rate constants for states up to v13 = 4 were based on the average values from all reactions. The rate constant for the (2,0) → (1,0) bending relaxation is in agreement with the published values from laser-induced fluorescent experiments; the rate constants for higher levels increase with v2. Our average rate constant for the (0,1) → (2,0) stretch-to-bend conversion is somewhat smaller but falls within the uncertainty limit of the published value. The average rate constants for the stretch-to-bend process for (01), (02), (03), and (04) stretching states are (4.3 ± 0.8) × 10−14, (7.7 ± 1.1) × 10−14, (14.3 ± 4.2) × 10−14, and (20.6 ± 6.2) × 10−14 cm3 molecule−1 s−1, respectively.

The bending force constant associated with formation water that is selected for the potential energy surface describing the OH/OD + GeH4 reaction is shown to be important for the degree of bending excitation of H2O and HOD.

The gas-phase unimolecular reactions of C

The five unimolecular HX and DX (X = F, Cl) elimination pathways of CD

The recombination of CF

The recombination of ·CHF

Chemically activated C

Stimulated emission (SE) induced by pulsed two-photon excitation of the 6p′[1/2]0, 6p′[3/2]2, 7p[1/2]0, 7p[3/2]2, and 7p[5/2]2 states of the Xe atom has been studied. Spectra of SE were recorded in the 800–3500 nm region, which covers the 6p′, 7p → 7s (2500–3500 nm), 6p′, 7p → 5d (1000–2000 nm), 7s → 6p (1200–1900 nm) transitions, as well as the near-IR 6p → 6s (800–1000 nm) transitions. It is shown that excitation of the 7p states results in radiative cascade via the 7s states, 7p → 7s → 6p, although at least one case of cascading via the 5d states is also observed. Spectra of SE induced by excitation of the 6p′ states are dominated by the 6p′ → 6s′ transitions in the near IR and the 6p′ → 5d[1/2]1 → 6p[1/2]1 → 6s[3/2]1 cascade; the 6p′ → 7s → 6p cascade is also observed, although the secondary 7s → 6p emission is rather weak in comparison with excitation of the 7p states.