The H+N2O→OH(2ΠΩ,υ′,N′)+N2 reaction: OH rotational angular momentum polarization

Abstract

The OH state-resolved angular momentum polarization generated by the H+N2O reaction has been investigated at a mean collision energy of 1.5 eV. The data were obtained under room temperature bulb conditions using 225 nm photolysis of H2S to generate translationally excited H atoms, and employed Doppler-resolved laser induced fluorescence to probe the nascent OH reaction products. The measurements revealed the OH rotational angular momentum, j′, to be aligned in the scattering plane (i.e., in the plane containing the reactant and product relative velocity vectors, k and k′). Furthermore, j′ was found to be preferentially aligned parallel to k′, particularly for lower OH rotational states. Out-of-plane torsional forces have been shown, therefore, to play an important role in generating OH rotation as the fragments separate. The new data are discussed in light of previously published studies of the title reaction, both from our own laboratory, and from those of other workers. Insight into the reaction mechanism is provided by comparison with the photodissociation dynamics of HN3, which helps, in particular, to clarify the origin of the propeller-like OH rotational angular momentum polarization.

Theoretical studies of product polarization and state distributions of the H+HCl reaction

“…Since the pioneering work of Fano and Macek [1], Herschbach and coworkers [2] and of Blais and Truhlar [3], substantial progress has been made during the past several years in the field of chemical reaction stereodynamics . With the development in new experimental techniques, such as laser-induced chemiluminescence [8], polarized laser-induced fluorescence [9], core extraction combined with resonance-enhanced multiphoton ionization (RE-MPI) [10,11], and doppler resolved laser-induced fluorescence [12,13], it is becoming increasingly Chemical Physics 283 (2002) [463][464][465][466][467][468][469][470][471][472] www.elsevier.com/locate/chemphys clear that product rotational polarization can provide detailed mechanistic information. One important step in the theoretical progress is the introduction of the concept of polarization dependent differential cross-sections (PDDCSs) by Shafer-Ray et al [14].…”

Product state resolved stereodynamics: Rotational polarization of OH(2Π;υ′,N′,Ω,f ) scattered from the reaction, H+CO2→OH+CO

“…13,28 The best fit plots, superimposed upon the experimental composite profiles in Fig. 2, allow construction of the set of polarization dependent differential cross-sections ͑PDDCSs͒,…”

“…The data analysis follows the procedures described in the accompanying paper 28 and only an outline is presented here.…”

“…dependent, Doppler-resolved LIF spectral profiles recorded under alternative photolysis-probe laser propagation and polarization geometries. Linear combinations of these were constructed, using procedures described elsewhere, 12,13,28 in order to generate the sets of composite Doppler profiles,…”

“…18 Indeed their energy distributions peaked at around twice the estimates reported earlier, 23,24 which were based upon direct LIF measurements of the scattered CO ͑necessarily, averaged over the quantum state distribution in the scattered OH͒. Comparisons between the dynamical behavior of reaction ͑1͒ and of the related, but strongly exothermic, reaction that follows: [25][26][27][28] suggest the possibility that the ''missing'' population might be associated with CO molecules scattered into highly excited rotational levels, that remained undetected in the LIF experiments. 18 The product rotational angular momentum distributions, both scalar and vectorial, reflect the stereodynamics of the collisions that produce them-the prime focus of the present investigation.…”