H+D2 reaction dynamics. Determination of the product state distributions at a collision energy of 1.3 eV

Abstract

Two‐photon resonance, three‐photon ionization has been used to determine the HD product internal state distribution formed by the reaction of fast H atoms with thermal D₂ molecules. A mixture of HI and D₂ is irradiated by a 266 nm laser pulse to dissociate the former, giving a center‐of‐mass collision energy of about 1.30±0.04 eV for H+D₂. After a sufficiently short delay to ensure essentially collision‐free conditions, a second laser is fired which causes multiphoton ionization of individual HD quantum states as well as D atoms, depending upon the choice of wavelength. Reaction occurs in a well‐defined effusive flow which emerges from a glass orifice placed between the acceleration plates of a differentially pumped time‐of‐flight mass spectrometer. Ion signals are referenced to those obtained from HD or D produced in an auxiliary microwave discharge. Relative formation rates are reported for HD(v=1, J=0–6) and HD(v=2, J=0–6). Nascent D atoms are also observed and an upper limit is placed on the production of HD(v=3). Rotational surprisal plots are found to be linear for the HD product state distribution yielding a slope of θ_R=5.1 for HD(v=1) and θ_R=4.7 for HD(v=2). These are extrapolated to provide full distributions for HD(v=0–2, J=0–6). The present product state distributions are compared with the recent experimental data of Gerrity and Valentini as well as with the quasiclassical trajectory calculations of Blais and Truhlar.