H. H. Harris

Rotational excitation in the electron impact ionization of supercooled N2

Electrons of controlled energy have been used to ionize and electronically excite N2 cooled to a translational temperature of <2u2009°K in a supersonic expansion either of pure N2 or 10% N2/Ar. This source likely provides N2 molecules ’’frozen out’’ in their N′′ = 0 and 1 rotational levels. The rotational state distribution of Bu20092Σ+uN+2 was determined by monitoring the rotationally resolved emission spectrum. Observation showed that even at high (∼500 eV) impact energies, the N+2 rotational distributions are inconsistent with selection rules (ΔN = ±1) for dipole excitation from N′′ = 0 and 1. For lower electron impact energies the angular momentum content of the excited N+2 ion increases sharply. These observations are rationalized by a model which invokes interactions between the ion and the ejected electron.

Dynamic model for vibronic excitation in low energy atom-molecule collisions☆

Abstract Product state distributions from low energy He + ue5f8N 2 and N + 2 ue5f8He collisions are presented. These data, obtained from collision-produced emission spectra, show severe deviations from Franck-Condon behavior which cannot be solely the result of molecular distortion arising from electrodynamic effects. A model based on consideration of the short-range interaction between the collision partners is proposed.

Luminescence from He+O2 collisions at low energy☆

The emission spectrum resulting from He+ue5f8O2 collisions in the kinetic energy range 25–400 eV has been measured between 1940 and 8500 A. The results show that highly endoergic charge transfer processes dominate the spectrum, although exoergic processes with excited O2+ production also occur. The nearly resonant charge exchange process yielding ground state He atoms and O2+[c 4Σu−(v=0)] does not occur with high probability.

Production of excited OD+ in O+−D2 collisions at low relative energies (below 4 eV)

The energetics of OD+ ions formed in collisions of ground state O+ with room temperature D2 molecules have been studied at relative energies in the range 0.76–3.58 eV using ion beam techniques. Excited electronic states of OD+ are inaccessible below about 1.3 eV, so that product internal energy must be vibrational‐rotational excitation of ground state (X 3Σ)OD+ below this energy. It was found that OD+ is formed with internal energy over the entire energy range. The spectator stripping mechanism seems to predominate over the entire energy range.

Product state distributions from CO2+ −H2 electron transfer

Abstract Emission from excited CO + ions resulting from CO 2+ −H 2 charge transfer collsions have been analyzed to yield vibrational state distributions of these products. These state distribution and the observed spectra have been compared to model spectra calculated from known CO and CO + potential energy curves and a recently proposed semi-empirical curve for CO 2+ . The model calculations which depend on this CO 2+ curve do not adequately reproduce the data.

Rydberg excitation of NO IN H+NO collisions near threshold

Abstract Emission from Rydberg states of NO molecules has been observed in H + ue5f8NO collisions at relative energies as low as 10 eV. Agreement between the observed NO γ band spectrum and a model spectrum based on vertical electronic transitions indicate that a relatively long range interaction produces these excitations. Collisions between protons and N 2 , CO and O 2 molecules produced no neutral molecule emissions in the range 190–800 nm; the apparently anomalous behavior of NO is interpreted in terms of molecular electronic structure.

Cd II excitation in slow He+‐Cd and He+2‐Cd collisions

Cross sections for production of excited states of Cdu2009II resulting from He+‐Cd and He+2‐Cd collisions are reported. These data suggest that high‐pressure (∼ atmospheres) operation of a He‐Cd laser in which pumping is achieved by charge‐transfer excitation with reactant He+2 might be possible. Selective population of the (4d)9(5s)2u20092D3/2 level in He+2‐Cd collisions produces enhancement of the 325.0‐nm line relative to the 441.6 nm.

Post-threshold behavior for co+ collision-induced dissociation

Abstract The relative cross sections for the collision-induced dissociation of CO + on five rare gases have been measured near threshold. The data are compared with the recent statistical theory of Rebick and Levine in the energy range 0–2 eV above threshold. In this energy range, no one form of the Rebick—Levine theory fits all of the data. Agreement with the theory improves as the mass of the target atom increases.

On the unimolecular isomerization of methyl isocyanide after hot tritium substitution

The Bunker formulation of RRKM theory is used to investigate the yields of CH2TCN and CH2TNC after the substitution of tritium for hydrogen on methyl isocyanide. To rationalize experimental data, large amounts of rotational energy are required at the last collision where either the rate coefficients for the forward and reverse reactions are comparable to the mean free time. This would imply either that the substitution reaction produces even larger amounts of rotational excitation than was previously expected (by typically occurring at larger impact parameters) or that rotational energy is not transferred to collision partners as effectively as in collisions near thermal energy.