15min:

D. FORTHOMME, C. P. MCRAVEN, T. J. SEARS, G. E. HALL, Chemistry Department, Brookhaven National Laboratory, Bldg. 555A, P.O. Box 5000, Upton, NY 11973, USA.

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Selected isolated rotational transitions in the 1-0 band of the red A² -X^{2 +} system in CN have been recorded with transient frequency modulation spectroscopy as a function of argon pressure up to 0.2 atmospheres at room temperature. Line shapes were fit using Fourier transforms of a parameterized time correlation function, including Doppler and velocity-dependent collisional broadening, and collisional shifts. Deviations from Voigt line shapes can be equally well fit by modeling the narrowing with a speed-dependent collision model or with a velocity-changing collisional narrowing model. Pressure broadening coefficients were observed with little rotational state dependence, in the range of 0.070 - 0.075 cm^-1 atm^-1. In contrast, a much stronger rotational state dependence is observed for both pressure-dependent blue shift coefficients and the narrowing parameters. No asymmetry in the pressure broadening was observed; any possible speed-dependence to the frequency shift was too small to be detected in these measurements.

Acknowledgments: Work at Brookhaven National Laboratory was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences.