Laser spectroscopy of the nu(1)+3 nu(3) absorption band in (C2H2)-C-12. I.Pressure broadening and absolute line intensity measurements

We have developed a Ti:Sa autoscan laser spectrometer and used it to perfor m a detailed investigation of individual line profiles in the nu(1)+3 nu(3) band of (C2H2)-C-12. Pressure self-broadening effects were measured for mo st lines with J " values ranging from 0 to 22, and for pressures between 10 and 600 Torr. The high-pressure data points (p > 250 Torr) are fitted sati sfactorily by a Voigt profile. Line narrowing, characterized by an underest imation of the Lorentz contribution to the Voigt profile, was observed for the low pressures range (p < 150 Torr), indicating the influence of molecul ar confinement. The two usual limit models (soft and hard collisions) were fitted to the observed line shapes in order to extract more precise informa tion concerning the pressure broadening. The present results confirm the ab sence of strong vibrational dependence in the self-broadening coefficients. Absolute line intensities are also determined in the fitting procedure. No significant differences were found for the two pressure domains if the app ropriate model in each range is used. (C) 1999 American Institute of Physic s. [S0021-9606(99)00141-5].