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Notes: An experimental investigation of the rotational-state dependence of intermolecular interactions for dipole–dipole systems was performed with the aid of light-induced drift. Data are presented of the relative change in collision rate upon excitation, Δν/ν, of HF with respect to polar and nonpolar collision partners (CH3F, CH3Cl, HCl, OCS, and CH4, H2, CO2, respectively). A continuously tunable color-center laser was used to rovibrationally excite HF in the fundamental vibrational band (v=0→1). Both P- and R-branch excitations were studied, with the rotational quantum number ranging from J=0 to 6. By combining Δν/ν for all pairs of P(J) and R(J−1) transitions, the separate v and J dependencies of the collision rate ν are obtained. It is found that for HF–CH3F ν decreases by more than 40%, and for HF–CH4 by only 4%, as J increases from 0 to 6. These data show that the familiar 1/r3 dipole–dipole interaction is highly J dependent. We attribute this to the increased averaging-out of the dipole–dipole interaction as the rotational quantum number increases. A theoretical treatment based upon the first Born approximation for the total cross section of two rotating dipolar molecules is proposed. Comparison between measurements and theoretical results shows good agreement. © 1997 American Institute of Physics.

Notes: A one-dimensional fluid model for radio-frequency glow discharges is presented which describes silane/hydrogen discharges that are used for the deposition of amorphous silicon (a-Si:H). The model is used to investigate the relation between the external settings (such as pressure, gas inlet, applied power, and frequency) and the resulting composition of the gas and the deposition rate. In the model, discharge quantities such as the electric field, densities, and fluxes of the particles are calculated self-consistently. Look-up tables of the rates of the electron impact collisions as a function of the average electron energy are obtained by solving the Boltzmann equation in a two term approximation for a sequence of values of the reduced electric field. These tables are updated as the composition of the background neutral gas evolves under the influence of chemical reactions and pumping. Pumping configuration and gas inlet are taken into account by adding source terms in the density balance equations. The effect of pumping is represented by an average residence time. The gas inlet is represented by uniformly distributed particle sources. Also the radial transport of neutrals from the discharge volume into the discharge-free volume is important. As the fluid model is one dimensional, this radial transport is taken into account by an additional source term in the density balance equations. Plasma–wall interaction of the radicals (i.e., the growth of a-Si:H) is included through the use of sticking coefficients. A sensitivity study has been used to find a minimum set of different particles and reactions needed to describe the discharge adequately and to reduce the computational effort. This study has also been used to identify the most important plasma-chemical processes and resulted in a minimum set of 24 species, 15 electron-neutral reactions, and 22 chemical reactions. In order to verify the model, including the chemistry used, the results are compared with data from experiments. The partial pressures of silane, hydrogen, disilane, and the growth rate of amorphous silicon are compared for various combinations of the operating pressure (10–50 Pa), the power (2.5–10 W), and the frequency (13.56–65 MHz). The model shows good agreement with the experimental data in the dust free α regime. Discharges in the γ′ regime, where dust has a significant influence, could not be used to validate the model. © 1997 American Institute of Physics.