Collision Cross Sections For Excitation Research Articles

Low-Energy Inelastic Na + H Collisions

We report full quantum scattering calculations for near-threshold collision cross sections for excitation of Na by H. The calculations include contributions from transitions between all singlet states up to and including the ionic state (ion-pair production). The dynamics calculations are based on three sets of recent ab initio and pseudo-potential quantum-chemical calculations. Considerable sensitivity to the couplings employed is found.

Rotational excitation and de-excitation of interstellar ammonia in collisions with helium

We present quantal close coupling (CC) calculations of rotational excitation rate coefficients of ammonia NH3 by collision with He. Calculations have been performed with the new accurate interaction potential energy surface of Hodges and Wheatley (2001 J. Chem. Phys. 114 8836). Comparison with previous theoretical and experimental studies is performed. The MOLSCAT molecular collision code of Hutson and Green has been used at two different levels of approximation. We find that the coupled states (CS) approximation gives results for the rotational excitation collision cross sections which are consistent with CC calculations. The sensitivity to the potential energy surface is emphasized.

Boltzmann equation analysis of electron-molecule collision cross sections in water vapor and ammonia

Sets of electron-molecule collision cross sections for H2O and NH3 have been determined from a classical technique of electron swarm parameter unfolding. This deconvolution method is based on a simplex algorithm using a powerful multiterm Boltzmann equation analysis established in the framework of the classical hydrodynamic approximation. It is well adapted for the simulation of the different classes of swarm experiments (i.e., time resolved, time of flight, and steady state experiments). The sets of collision cross sections that exist in the literature are reviewed and analyzed. Fitted sets of cross sections are determined for H2O and NH3 which exhibit features characteristic of polar molecules such as high rotational excitation collision cross sections. The hydrodynamic swarm parameters (i.e., drift velocity, longitudinal and transverse diffusion coefficients, ionization and attachment coefficients) calculated from the fitted sets are in excellent agreement with the measured ones. These sets are finally used to calculate the transport and reaction coefficients needed for discharge modeling in two cases of typical gas mixtures for which experimental swarm data are very sparse or nonexistent (i.e., flue gas mixtures and gas mixtures for rf plasma surface treatment).

Need for fundamental data in atomic fluorescence spectrometry

This paper discusses the needs for fundamental data in atomic fluorescence spectrometry and addresses the diagnostic and theoretical aspects, on the one hand, and the analytical aspects, on the other. Transition probabilities, collision cross sections for excitation and deexcitation, lifetimes, quantum efficiencies, and ionization and recombination cross sections are shown to be the essential fundamental data needed for diagnostic and theoretical studies. It is argued that, analytically, detailed knowledge is indispensable about the excitation and emission spectra as observed with a tunable dye laser as excitation source and a versatile atomizer, such as an ICP, as fluorescence cell.

Ionization behind strong normal shock waves in argon

The ionization of argon by strong normal shock waves is studied. The conservation equations are solved to yield the plasma behavior behind the shock wave front. Very good agreement is obtained between experimental findings and the present numerical results for the electron number density, plasma density, and degree of ionization, especially at the electron avalanche region of the relaxation zone. The high accuracy of the present numerical solutions in reproducing the electron avalanche is attributed to the use of accurate threshold collision cross sections for excitation of argon by electron collisions. To support this claim it is demonstrated that if different assumptions were used to describe the ionization process, then the computed results would be different only upstream of the electron avalanche region, i.e., it is shown that the proposed model for ionizing shock waves enables a highly accurate reproduction of the electron avalanche but is less accurate in predicting its exact location.

Energy-Loss Spectra and Collision Cross Sections for Impact of 20-120-keV Positive Ions on Molecular Nitrogen

Inelastic energy-loss spectra induced by impact of ${\mathrm{H}}^{+}$, ${\mathrm{H}}_{2}^{+}$, and ${\mathrm{Ar}}^{+}$ on ${\mathrm{N}}_{2}$ have been measured at incident ion energies of 20-120 keV, with an energy resolution of about 2 eV. Prominent peaks are observed at energy losses of 9.5 and 13.8 eV. The first of these is well resolved and is attributed to excitation of the Lyman-Birge-Hopfield (LBH) system of ${\mathrm{N}}_{2}$. The peak at 13.8 eV is believed due primarily to excitation of the $b^{1}\ensuremath{\pi}_{u}$ band of the Worley-Jenkins series. The locations of these features on the energy-loss scale do not agree with results of the electron impact work of others and, in general, show trends with projectile velocity that are consistent with an assumed enhancement of excitation to higher vibrational states with the heavier particles. Collision cross sections for excitation of the two peaks are presented, as well as the total ionization cross section and the cross section for total inelastic processes in the case of proton impact.

Impact-Parameter Calculation of Hydrogen-Hydrogen Double-Excitation Collisions

Hydrogen-hydrogen double excitation collision cross sections computed by impact parameter method, using Born and two state approximations