The influence of rotation and vibration on the reactivity and the dynamics of the reaction X+HCN(ν1,ν2,ν3,J)→HX+CN(v,J) with X=H, Cl has been studied. The HCN molecule is prepared in a specific rovibrational level by IR/VIS overtone excitation in the wavelength region 6500–18 000 cm−1. The H atoms are generated by laser photolysis of CH3SH at 266 nm, the Cl atoms are formed in the photodissociation of Cl2 at 355 nm. The CN products are probed quantum state specifically by laser-induced fluorescence (LIF). For low rotational states of HCN, the reactivity of Cl and H is independent of the initial rotational state. However, an enhancement in reactivity of the Cl+HCN reaction is observed when the time of rotation becomes comparable to the passing time of the Cl atom. The reaction of Cl as well as of the H atom with HCN shows strong mode specific behavior, implying a simple direct reaction mechanism, which is also supported from Rice–Ramsperger–Kassel–Marcus (RRKM) calculations. An increase in CH stretch vibration increases both the reaction rate and the CN product vibration. Channeling energy in CN stretch vibration has only a minor effect on the reactivity and the CN product vibration even decreases. Trajectory calculations of the H+HCN system agree with the experimental results. The dependence of reaction rates on reactant approach geometry is investigated by preparing aligned reactants using linear polarized light. The CN signal is markedly influenced by the prepared alignments (steric effect). The experimental results suggest that the reaction of hydrogen and chlorine atoms with vibrationally excited HCN proceeds mainly via a collinear transition state, but the cone of acceptance is larger for chlorine atoms.
State-to-state rotational energy transfer of ground state NH(X 3Σ−,v=0,J,N) in collisions with He and N2 is studied. A complete inversion between the metastable NH(a 1Δ) state and the NH(X 3Σ−) state is generated via the photodissociation of hydrazoic acid at a wavelength of 266 nm. Single state NH(X 3Σ−,v=0,J,N) is generated by applying the stimulated emission pumping technique using the strongly forbidden NH(a 1Δ→X 3Σ−) intercombination transition around 794 nm. The ground state NH(X 3Σ−,v=0,J,N) distribution is probed with respect to all quantum states using laser induced fluorescence varying delay times and pressures. The collision induced energy transfer between the different rotational and spin levels is extensively studied and two comprehensive sets of rate constants for vibrationally elastic and rotationally inelastic collisions with He and N2 as collision partners are given which include the effect of multiple collisions. We find propensities for (ΔN=0,Δi=±1) and (ΔN=±1,Δi=0) transitions where N represents the quantum state for nuclear rotation and i represents the index of the spin component Fi. The rotational relaxation for N2 as a collision partner occurs on the average three times faster than the rotational relaxation with He as a collision partner. The energy dependence of the transition efficiency for only the nuclear rotational quantum number N obeys an energy-gap law for both He and N2.
State-to-state energy transfer of NH (X 3 Σ − ,v=0,J,N) in collisions with He and N 2 State-to-state rate constants for the rotational relaxation of CH (B 2 Σ − ,v=0,J) in inelastic collisions with Ar State-to-state rotational energy transfer of ground state NH(X 3 ⌺ Ϫ ,vϭ0,J,N) in collisions with Ne is examined. NH is exclusively generated in the metastable NH(a 1 ⌬) state via photodissociation of hydrazoic acid at a wavelength of 266 nm. The strongly forbidden NH(a 1 ⌬→X 3 ⌺ Ϫ ) intercombination transition around 794 nm is used to generate single state NH(X 3 ⌺ Ϫ ,vϭ0,J,N) applying the stimulated emission pumping technique. The ground state radicals are detected after a certain delay time with laser induced fluorescence ͑LIF͒ using the intense NH(A 3 ⌸←X 3 ⌺ Ϫ ) transition around 336 nm with respect to all quantum states. The collision induced energy flux between the different rotation and spin levels is studied in detail and a comprehensive set of state-to-state rate constants for inelastic collisions of NH(X 3 ⌺ Ϫ ,vϭ0,J,N) with Ne up to Nϭ7 which include the effect of multiple collisions is given. The state-to-state rate constants are obtained by the use of an iterative integrated profiles method. We find a propensity for (⌬Nϭ0, ⌬i ϭϮ1) and (⌬NϭϮ1, ⌬iϭ0) transitions where N represents the quantum state for nuclear rotation and i represents the index of the spin component F i . In most cases the energy transfer which changes the spin component and conserves the nuclear rotation quantum number N (⌬Nϭ0, ⌬i ϭϮ1), is the most effective energy transfer in collisions with Ne. The energy dependence of the transition efficiency concerning only the nuclear rotation quantum number N obeys an energy-gap law ͑EGL͒.
A new method is presented to examine state-to-state rotational energy transfer in ground state NH(X 3Σ−,v=0,J,N). NH(X 3Σ−) is generated via state selective stimulated emission pumping using the strongly forbidden NH(a 1Δ→X 3Σ−) intercombination transition around 794 nm after foregoing photodissociation of HN3 at a wavelength of 266 nm. Products are detected by laser induced fluorescence (LIF). Chemically relevant collision dynamics including spatial processes can be studied for the first time in v=0 of the electronic ground state. State-to-state rate constants for inelastic collisions of NH(X 3Σ−,v=0,J=3,N=3) with Ne are presented.
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