Dahv A. V. Kliner

Comparison of experimental and theoretical integral cross sections for D+H2(v=1, j=1)→HD(v’=1, j’)+H

We have measured the nascent HD(v’=1, j’) product rotational distribution from the reaction D+H2(v, j) in which the H2 reagent was either thermal (v=0, j) or prepared in the level (v=1, j=1) by stimulated Raman pumping. Translationally hot D atoms were obtained by uv laser photolysis of DBr or DI. Photolysis of DBr generated D atoms with center‐of‐mass collision energies (Erel) of 1.04 and 0.82 eV, which corresponded to the production of ground state Br and spin–orbit‐excited Br*, respectively. The Erel values for DI photolysis were 1.38 and 0.92 eV. Quantum‐state‐specific detection of HD was accomplished via (2+1) resonance‐enhanced multiphoton ionization and time‐of‐flight mass spectrometry. Vibrational excitation of the H2 reagent results in substantial rotational excitation of the HD(v’=1) product and increases the reaction rate into v’=1 by about a factor of 4. Although the quantum‐mechanical calculation of Blais et al. [Chem. Phys. Lett. 166, 11 (1990)] for the D+H2(v=1, j=1)→HD(v’=1, j’)+H product ...

Quantitative determination of H2, HD, and D2 internal‐state distributions by (2+1) resonance‐enhanced multiphoton ionization

The relationship between quantum‐state populations and ion signals in (2+1) resonance‐enhanced multiphoton ionization (REMPI) detection of H2, HD, and D2 via the E, F 1Σ+g (v’E=0, J’=J‘)–X 1Σ+g (v‘,J‘) transition is determined by calibration against a thermal effusive source. Correction factors are obtained for 102 rovibrational levels for v‘=0, 1, and 2 and J‘ ranging from 0 to 17. Within a given v‘, rotational correction factors are nearly unity except for the highest J‘ levels. The vibrational correction factors vary with v‘; (2+1) REMPI detection is 2–3 times more sensitive to v‘=1 and 2 than to v‘=0. Experimental correction factors are compared with those derived from a theoretical calculation of the two‐photon transition moments by Huo et al. [J. Chem. Phys. 95, xxxx (1991)]. In general, the agreement is excellent, which suggests that theoretical correction factors may be used when experimental ones are unavailable.

D+H2(v=1, J=1): Rovibronic state to rovibronic state reaction dynamics

We have studied the D+H2(v=1, J=1)→HD(v’,J’)+H reaction at ∼1.0 eV center‐of‐mass collision energy. The H2 is prepared in (v=1, J=1) by stimulated Raman pumping and the HD(v’=1, J’) rotational distribution is measured by (2+1) resonance‐enhanced multiphoton ionization. Vibrational excitation of the H2 reagent results in substantial rotational excitation of the HD(v’=1) product, the fraction of the available energy appearing as product rotation increasing from gR=0.17 for the D+H2(v=0, J thermal) ‘‘unpumped’’ reaction to gR=0.34 for the D+H2(v=1, J=1) ‘‘pumped’’ reaction. We estimate that the reaction cross section into HD(v’=1) is at least 4 times larger for the pumped than the unpumped reaction.

The D+H2 reaction: Comparison of experiment with quantum-mechanical and quasiclassical calculations

Abstract We have measured the HD( v ′ = 1, J ′) rotational distribution from the D + H 2 reaction at a center-of-mass collision energy of about 1.05 eV. The experimental data are compared to distributions derived from two quantum-mechanical (QM) calculations and from a quasiclassical trajectory (QCT) calculation. We find essentially perfect agreement between experiment and the QM calculations, while the QCT results are too hot rotationally.

Measurement of relative state-to-state rate constants for the reaction D+H2(v,j)→HD(v',j')+H

We have measured state‐to‐state integral rate constants for the reaction D+H2(v,j) →HD(v’=0,1,2;j’)+H, in which the H2 reagent was either in the ground state, H2(v=0,j), or prepared in the first excited vibrational state, H2(v=1, j=1), by stimulated Raman pumping. Translationally hot D atoms were produced via UV photolysis of DI, generating two center‐of‐mass collision energies corresponding to the two I atom spin–orbit states. Resonance‐enhanced multiphoton ionization and time‐of‐flight mass spectrometry were employed to detect the nascent HD product in a quantum‐state‐specific manner. Two experimental geometries were used: (1) a probe‐laser‐induced geometry, in which the same laser both initiated the reaction, by photolysis of DI, and detected the HD and (2) an independent‐photolysis‐source geometry, in which photolysis of DI was carried out by an independent laser. We find that vibrational excitation of the H2 reagent results in substantial HD rotational excitation for each product vibrational state, a...

The H+para-H2 reaction : influence of dynamical resonances on H2(v'=1,j' =1 and 3) integral cross sections

We have measured integral rate constants for the reaction H+para‐H2→H2(v’=1, j’=1 and 3)+H at 11 center‐of‐mass collision energies (Erel) between 0.88 and 1.01 eV, a region in which dynamical scattering resonances are present. We have also measured the H2(v’ = 1, j’ = 3)/H2(v’ = 1, j’ = 1) population ratio at two additional values of Erel outside of this range. Tunable uv laser photolysis of HI was used to generate translationally hot H atoms of variable kinetic energy. Quantum‐state‐specific detection of the H2 reaction product was accomplished via (2+1) resonance‐enhanced multiphoton ionization and time‐of‐flight mass spectrometry. The integral rate constants have a smooth dependence on Erel, in agreement with the recent quantum‐mechanical (QM) calculations of Zhang and Miller and contrary to the experimental results of Nieh and Valentini. The QM results are in nearly perfect agreement with the present measurements for the dependence on Erel of both the integral rate constants and the H2(v’ = 1, j’ = 3)...

The H+D2 reaction: Quantum‐state distributions at collision energies of 1.3 and 0.55 eV

We have studied the H+D2 →HD+D reaction using thermal D2 (∼298 K) and translationally hot hydrogen atoms. Photolysis of HI at 266 nm generates H atoms with center‐of‐mass collision energies of 1.3 and 0.55 eV, both of which are above the classical reaction barrier of 0.42 eV. The rovibrational population distribution of the molecular product is measured by (2+1) resonance‐enhanced multiphoton ionization (REMPI). The populations of all energetically accessible HD levels are measured. Specifically, we observe HD(v=0, J=0–15), HD(v=1, J=0–12), and HD(v=2, J=0–8). Of the available energy, 73% is partitioned into product translation, 18% into HD rotation, and 9% into HD vibration. Both the rotational and vibrational distributions are in remarkably good agreement with quasiclassical trajectory (QCT) calculations, though the calculated rotational distributions are slightly too hot. We discuss factors contributing to the success of the QCT calculations.

The H+D2 reaction: “prompt” hd distributions at high collision energies

Abstract Probe-laser-induced (“prompt”) reaction of H + D 2 was observed in a mixture of HI and D 2 using (2 + 1 ) REMPI detection of the HD product. Rotational distributions for HD (ν= 0–3 ) of the prompt reaction are reported here, corresponding to center-of-mass collision energies of 1.20–1.65 eV and 1.95–2.40 eV. The measurements of the HD(ν= 3, J ) product probe a previously inaccessible region of the potential energy surface for the title reaction. At these energies, the total reaction cross sections have been both measured and calculated, but quantum state specific theoretical predictions are not yet available.

The H+D2 reaction: HD(ν=1, J) and HD(ν=2, J) distributions at a collision energy of 1.3 eV

Abstract Complete quantum state distributions for HD (ν= 1) and HD (ν= 2) are obtained by photolyzing HI at 266 nm in the presence of D 2 and detecting the nascent HD product via (2+1) resonance-enhanced multiphoton ionization (REMPI). Calibration against an effusive oven source (⩽ 1800 K) yields any necessary correction factors to relate the integrated ion signals to relative quantum state populations. Comparisons are made with previously published experimental results of Gerrity and Valentini and of Marinero, Rettner and Zare as well as with quasiclassical trajectory calculations of Blais and Truhlar. Although the combined experimental data agree well with the quasiclassical trajectory calculations of Blais and Truhlar, it is suggested that the latter yield rotational distributions which are slightly too hot.

Construction of a shuttered time‐of‐flight mass spectrometer for selective ion detection

By placing a pulsed, high‐voltage steering plate between the ion source and detector in a time‐of‐flight mass spectrometer, the signal‐to‐noise ratio of the mass of interest is improved by more than an order of magnitude. This improvement arises from (1) suppression of ions of other masses formed at the same time as the ion of interest and (2) suppression of ions formed at different times and different locations whose arrival time at the detector is nearly coincident with the mass of interest. The advantages of this simple device are demonstrated in the detection of molecular hydrogen in the presence of other species.