John S. Winn

Dynamics of the O+–H2 reaction. II. Reactive and nonreactive scattering of O+(4S3/2) at relative energies above 13 eV

We report velocity vector distributions for the reactive and nonreactive scattering of O+ by H2, D2, and HD in the relative energy range 13–50 eV. Essentially no very small angle reactive scattering is observed for any of these systems. In the lower and intermediate parts of the energy range, the product of the O+(D2, D)OD+ reaction reaches a maximum intensity near 50°, and decreases somewhat at larger angles. This shape is maintained but with decreasing intensity from 15–30 eV relative energy. At higher energies, the distribution moves to larger angles and the intensity continues to drop. From 13–20 eV, OH+ from O+–HD collisions peaks near 35°, and has little intensity at larger angles, while the corresponding OD+ product rises to a broad miximum near 90°, and is only slightly less intense at larger angles. At relative energies above 13 eV the nonreactive scattering of O+ has a major component that corresponds to the elastic impulsive scattering of O+ from one atom of the target. Nonreactive scattering f...

Dynamics of the O+‐H2 reaction. I. Reactive scattering of O+(4S3/2) at relative energies below 15 eV

Product velocity vector distributions show that the reaction O+(H2,H)OH+ and its isotopic variations proceed from ground state reactants to predominantly electronic ground state products via a direct interaction. Spectator stripping is a prominent feature at the lower relative energies of collision, but the stripping peak is lost at energies where the internal excitation of OH+ (3Σ−) makes it unstable to dissociation. Production of forward scattered electronically excited OH+, probably in the 1Δ state, is observable when the initial relative energy is high enough that OH+(3Σ−) formed by spectator stripping is unstable with respect to dissociation. At these relative energies, OH+ from HD is predominantly scattered into barycentric angles less than 90°, while the OD+ appears at approximately 90° at larger angles. The propensity for formation of OD+ at large angles can be understood in terms of general kinematic considerations which apply to collinear collisions.

Sequential impluse model of direct reactions

A model in which the reaction A(BC, C) AB occurs as the result of a sequence of two hard sphere elastic impulses between the A–B and B–C pairs is analyzed. It is shown that the limits of the product velocity vector distribution can be readily obtained from the analytic geometry of the impulse sequence, and that an analytical expression for the detailed product distribution for all mass combinations and energies can be deduced. The results show a propensity for processes in which the velocity of the C atom is changed very little and which therefore lead to products near the spectator stripping velocity. The angular distribution is dependent on, but relatively insensitive to, the ratio of the mutual hard sphere diameter of B and C to their bond distance. The predictions of the model are generally consistent with the features found in the experimental investigations of high energy ion–molecule reactions.

Recovery of the long range potential in BeAr+ by potential inversion methods

The results of the potential inversion methods of Dunham, Simons, Parr, and Finlan, Thakkar, Huffaker, and the Pade approximate technique are presented for the X 2Σ+ state of BeAr+. The method of Thakker is shown to yield reasonable behavior at long range, leading to an ion‐induced dipole interaction. A simple model potential is shown to provide a good description of the bonding in both the ground state and the A 2Πr state. The effective nuclear charge of Be+ is found to be 1.29 in the X state and 1.88 in the A state. Integration of the various potentials to determine the vibrational eigenvalues shows the superiority of the Thakkar and Huffaker methods and shows the three parameter model potential to be a very good representation of the true potential.

Laser-induced fluorescence of trapped molecular ions: the CH+A1Πâ†X1Σ+ system

The CH+ and CD+A1Πâ†�X1Σ+ absorption spectra have been obtained by laser excitation of these fragment ions. The ions are contained in a mass-selective quadrupole ion trap under collision-free conditions. The spectra therefore reflect the nascent internal-energy distributions of the ions, which were produced by electron impact on CH4(CD4) or C2H2(C2D2). Both parent gases gave virtually identical spectra; large rotational and vibrational excitation was observed. The equipment was also capable of measuring the radiative lifetime of CH+(CD+)A2Π(v= 0), and the measured value, 815 ns, is found to be in good agreement with theoretical calculations of this quantity.

Impulsive inelastic scattering of O+(4S) by isotopic hydrogen molecules

Abstract We present experimental evidence that at relative energies above 10 eV the non-reactive inelastic scattering of O + by H 2 , D 2 , and HD arises from impulsive elastic scattering of 0 + by individual H or D atoms. The relation of this impulsive non-reactive scattering to the reactive scattering from these systems is briefly discussed.

CHEMILUMINESCENT CHEMI-IONIZATION: Ar* + Ca AND THE CaAr+ EMISSION SPECTRUM

A flowing afterglow chemiluminescence apparatus has been used to analyze visible fluorescence in the Ar*(3P 20)+Ca(1S0) reaction. The rate constants for production of Ca+(2P 3/20) and Ca+(2P 1/20) were measured to be 1.6×10−10 and 3.2×10−11 cm3 molecule−1 sec−1, respectively. These results demonstrate a transfer of the total electronic angular momentum polarization in Ar* to the excited ion levels. The molecular band spectrum of the associative ionization product CaAr+(A 2Π) was observed. Molecular fluorescence constituted 14% of the total fluorescence from all ion products. This spectrum was analyzed with a model (exp‐Z4) potential, yielding, for the ground state X 2Σ+, Re = 2.8 A, ωe″ = 87 cm−1, and De″ = 1000 cm−1, and, for the A 2Π state, Re = 2.6 A, ωe′ = 200 cm−1, and De′ = 4900 cm−1. The nascent internal state distribution in CaAr+ is found to consist of a fairly narrow range of high vibrational levels.

Inelastic Scattering of Ne+ by H2 and D2

The reaction Ne+(H2, H)NeH+ is notable as a simple exoergic ion‐molecule reaction which has a very small rate constant, less than 8×10−12 cc/sec. We have studied the velocity vector distributions of Ne+ scattered nonreactively from H2 and D2 at a number of energies. There is no evidence for the occurrence of reactive or charge transfer collisions. The small angle (<90°) scattering is elastic, but there is large angle inelastic scattering of three types: vibrational and rotational excitation of hydrogen, collisional dissociation to Ne++H+H, and electronic excitation of hydrogen to B 1Σu+ and perhaps other states. The results are consistent with conclusions drawn from a molecular orbital correlation diagram for the (Ne‐H2)+ system.

Atomic iron chemiluminescence from Ar* (3P) collisions with Fe(CO)5

First observation of chemiluminescence resulting from collisional electronic energy transfer to a metal carbonyl are described. The process Ar* (3P)+Fe(CO)5→Ar+Fe*+5CO has been observed. (AIP)

Estimation of the dissociation energy of weakly‐bound molecules from spectroscopic data

Expressions for the dissociation energy of the Morse potential and the Lennard‐Jones (2n,n) potential are derived in terms of low‐order mechanical constants of diatomic molecules. These expressions are related to a more general series expansion of the potential, and a new expression for the dissociation energy of a weakly bound diatomic is derived. This expression contains Be’αe’ and the power of R−1 which leads a long‐range expansion of the potential. The expression is accurate to a few percent when compared to reliable experimental values and should be of value when only a limited number of spectral constants can be obtained from experiment.