Diode laser spectroscopic measurement and impact theoretical analysis of collision broadening of acetylene (nu(1)+3 nu(3)) band transitions

A near infrared diode laser spectrometer has been used for measurement of l ine shapes of the rotational transitions of the (v(1) + 3v(3))overtone-comb ination band of acetylene perturbed by oxygen and air. Pressure-broadening coefficients and line strength parameters are extracted from least squares fitting of the spectra with Voigt profiles. A detailed calculation of press ure-broadening coefficients for the self, nitrogen and oxygen broadening ca ses has been performed by using semi-classical impact theory based on quadr upolar and dispersion interactions. The relative importance of the intermol ecular interactions has been investigated and it is found that for these we ak interaction cases dispersive terms have a dominant role in line broadeni ng. This is more pronounced for the O-2-broadening case. We have included a ll the non-resonant terms till convergence is achieved. The cutoff paramete r b(0) of the Anderson procedure has been determined separately for each no n-resonant process. In order to include the orientation effect of the molec ules at the moment of collision we have considered an average kinetic colli sion diameter which sets the lower limit of b(0). This improves the result considerably and the calculated values are close to the observed results. T he J-dependence of the half width is also reported and shows decrease for l arge J-values.