Experimental study of the dynamics of the H+D2 → HD+D reaction at collision energies of 0.55 and 1.30 eV

Abstract

We report here experimental measurement of the nascent HD product quantum state distributions for the H+D2 → HD+D reaction. Pulsed laser photolysis of HI in an HI/D2 gas mixture produces hydrogen atoms giving H+D2 collision energies of 0.55 and 1.30 eV. Nanosecond-time-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy is used to record rotationally and vibrationally resolved spectra of the HD reaction product under nearly single-collision conditions. The spectra are analyzed to determine the nascent, single-collision HD product quantum state distributions. These distributions are compared to the results of related experiments by E. E. Marinero, C. T. Rettner, and R. N. Zare and to the results of recent quasiclassical trajectory calculations of N. C. Blais and D. G. Truhlar. Our results are in qualitative agreement with those of Marinero et al., but there are some quantitative differences. The trajectory calculations yield HD quantum state distributions which are very close to those we have measured. We find that our HD product quantum state distributions are fairly well summarized by a linear surprisal analysis with a rotational surprisal of 3.0 and a vibrational surprisal of 2.6. The quantum state distributions indicate that 71%±1% of the energy available to the products appears in translation, while 19%±2% is in HD rotation, and 10%±2% is in vibration. These results are discussed in terms of the dynamics of the reaction.

Dynamics study of the OH + NH3 hydrogen abstraction reaction using QCT calculations based on an analytical potential energy surface

“…Second, large tails in both distributions could be an artefact of the QCT method, because they tend to give rotational distributions that are hotter and broader than experiment and quantum-mechanical methods. [26][27][28][29][30][31] Note that these two effects have opposite behaviours, and tend to cancel.…”

CARS (coherent anti-Stokes Raman spectroscopy) diagnostics of discharges

“…la); 2) use several high pass dichroic mirrors immediately after the entrance window to remove its contribution (Fig. lb); 3) use a multiple pass arrangement to enhance the signal from the gas (Fig. lc).…”

“…[1][2][3][4][5], showing the potential for detection of species at low pressure with the difficult challenge of completing the measurement in precise synchronism with the photolysis pulse. In this area, the exchange between the experimenter and the theorist is far more rewarding.…”

Differential cross sections for H+D2→HD(v′=1, J′=1,5,8)+D at 1.7 eV

“…For example, theory 29,42,43 and experiment [44][45][46][47][48] agree that the hydrogen exchange reaction is largely adiabatic in regard to translation and vibration, i.e., translational ͑vibrational͒ energy in the reagents is efficiently converted into translational ͑vibrational͒ energy of the products. Therefore, our current ability to measure angular distributions for highly excited rovibrational states provides a further test of both approximate and exact dynamical theories on this reaction system for product states where unexpected effects may arise.…”