Pressure Line Broadening And Shifting of Water Vapor Overtones

Some overtone absorption lines of water vapor in the region around 12100 cm-1 have been examined by using a diode laser (DL) spectrometer [1]. The employed sources are commercially available double heterostructure AlxGa1-xAs DLs operating in "free-running" mode; still the high resolving power (~107) of the spectrometer permits the detection and the study of the absorption features of the molecules with a precision of less than 0.01 cm-1. Wavelength modulation spectroscopy (WMS) along with the 2nd harmonic detection techniques have been adopted in order to maximize the signal to noise ratio (S/N) and to extract the necessary informations either on the line width and on the line position for each resonance. The fit procedure has been critically analyzed in order to take into account the instrumental effects and the amplitude modulation (AM) always associated to the frequency modulation (FM) of these sources [2]. Collisional broadening and shifting coefficients by three different perturber gases have been measured at room temperature. The results are compared to those obtained by more expensive spectroscopic systems. 1. A. Lucchesini, S. Gozzini, C. Gabbanini, Eur. Phys. J. D, Vol. 8, 223-226 (2000) 2. M. De Rosa, A. Ciucci, D. Pelliccia, C. Gabbanini, S. Gozzini, A. Lucchesini, Opt. Commun., Vol. 147, 55-60 (1997)