Rovibronic state to rovibronic state reaction dynamics: O(3 P)+HCl(v=2,J)→OH(v′,N′)+Cl(2 P) Complete rotational distributions have been obtained for the CO produced following excitation of H 2 CO, HDCO, and D 2 CO near the S 1 origin. The CO was detected by vacuum ultraviolet laser-induced fluorescence. The distributions show a remarkable amount of rotational excitation, peaking at J = 42, 49, and 53 for H 2 CO, HDCO, and D 2 CO, respectively, with widths of 20-25 J units (FWHM). CO(v = 1) from H 2 CO photolysis has nearly the same rotational distribution as CO(v = 0). The population of CO(v = 1) is 14%±5% as large as the population of CO (v = 0), in good agreement with earlier measurements. Increased angular momentum of H CO is only partially transferred to CO, giving slightly wider rotational distributi~ns without changing the peak value. The rotational distributions are highly nonthermal, showing that energy randomization does not occur during the dissociation event. An approximate range of product impact parameters has been determined. The impact parameters are too large to be accounted for by forces along the directions of the C-H bonds. The hydrogen ~ppears to be most strongly repelled by the charge distribution a fraction of an A outside the carbon atom of the CO. The distribution of impact parameters and the internal energy of the hydrogen fragment apparently do not change significantly upon isotopic substitution. The absence of population in CO(J < 20) confirms the identity of CO(J > 25) as the long-lived intermediate in formaldehyde photodissociation.3032

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The reaction H+D2O was studied by intersecting a pulsed beam of HI with an effusive spray of D2O in a high vacuum chamber. Translationally hot H atoms were generated by UV photolysis of HI in the intersection volume, and the HD product of the reaction H+D2O was detected in a quantum-state-specific manner by (2+1) resonance-enhanced multiphoton ionization. Because the same UV laser beam was used to initiate the reaction and detect the product, the relative collision energy varied as a function of product state detected—∼2.8 eV for v′=0, ∼2.6 eV for v′=1, and ∼2.5 eV for v′=2. Under these conditions, approximately 35% of the available energy is partitioned into the internal modes of the HD product. For the products, the HD ‘‘new bond’’ receives 15 times more energy than the OD ‘‘old bond.’’ A significant amount of energy appears as HD vibration with v′=0 and 1 having comparable populations. The fraction of available energy partitioned into HD rotation, gR(v′), is found to be essentially independent of HD vibration. This invariance may be rationalized in terms of a counterbalancing of two mechanisms for rotational excitation of the HD product. We find qualitative agreement between recent quasiclassical trajectory calculations by Kudla and Schatz for the HD product internal-state distributions and the present experimental results.

Stimulated emission pumping state preparation and laser induced fluorescence state detection in the CN(B 2Σ+–X 2Σ+) violet system have been employed to study relaxation of single rotational states of CN(X 2Σ+, v=2) in collisions with He at 295 K. Approximately 2/3 of the value of the total removal rate constant for CN(X 2Σ+, v=2, N=2, 11, or 14) corresponds to changes in the rotational quantum number of ‖ΔN‖≤3 and a strong propensity is evident which favors even changes in N for ‖ΔN‖≤4. The measured rate constants are consistent with detailed balance, can be described with statistical power-gap and exponential energy-gap fitting functions and, where compared, are in accord with an IOS-based scaling function. No significant difference is found between a sum of state-to-state rate constants and separately measured total removal rate constants for N=2, 11, and 14. The total removal rate constants decrease monotonically between N=0 and N=41 to about 1/3 of their value at N=0.

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