David E. Adelman

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 ...

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)...

Integral rate constant measurements of the reaction H +D2O → HD(v’, j’)+OD

The reaction H+D2O was studied by intersecting a pulsed beam of HI with an effusive spray of D2O in a high vacuum chamber. Translationally hot H atoms were generated by UV photolysis of HI in the intersection volume, and the HD product of the reaction H+D2O was detected in a quantum‐state‐specific manner by (2+1) resonance‐enhanced multiphoton ionization. Because the same UV laser beam was used to initiate the reaction and detect the product, the relative collision energy varied as a function of product state detected—∼2.8 eV for v’=0, ∼2.6 eV for v’=1, and ∼2.5 eV for v’=2. Under these conditions, approximately 35% of the available energy is partitioned into the internal modes of the HD product. For the products, the HD ‘‘new bond’’ receives 15 times more energy than the OD ‘‘old bond.’’ A significant amount of energy appears as HD vibration with v’=0 and 1 having comparable populations. The fraction of available energy partitioned into HD rotation, gR(v’), is found to be essentially independent of HD vi...

Integral rate constant measurements of the reaction H + D2 → HD (v′ = 1, j′) + D at high collision energies

Abstract The reaction H + D 2 → HD ( v ′ = 1, j ′) + D was studied using two different experimental geometries: (1) a probe-laser-induced reaction geometry and (2) an independent-photolysis laser geometry. High-energy H atoms were generated by photolysis of HI which resulted in center-of-mass collision energies of 2.2 and 2.5 eV for geometries 1 and 2, respectively. The HD product was detected using (2 + 1) REMPI and time-of-flight mass spectrometry. The HD( v ′= 1, j ′) rotational distributions are presented; at this time no corresponding theoretical calculations are available for comparison.

Product internal‐state distribution for the reaction H+HI→H2+I

We have measured the nascent H2(v, j) product‐state distribution from the H+HI→H2+I abstraction reaction. Laser photolysis of HI at 266 nm generated translationally hot H atoms with center‐of‐mass collision energies of 1.61 and 0.68 eV in the ratio 64:36. Quantum‐state‐specific detection of the molecular reaction product was accomplished via (2+1) resonance‐enhanced multiphoton ionization and time‐of‐flight mass spectrometry. The H2 is formed with a high degree of internal excitation, including a vibrational population inversion between v=0 and v=1. Our product‐state distribution agrees closely with that of Aker, Germann, and Valentini where comparison is possible. Rotational population distributions derived from the quasiclassical trajectory calculations of Gonzalez and Sayos are generally too cold, whereas those of Aker and Valentini nearly reproduce the experimental distributions. Both calculations fail to predict, however, the observed vibrational inversion.