Semi-classical analysis of helium broadened acetylene (v_1 + 3v_3) band transitions measured by a NIR diode laser spectrometer

摘要

Helium-broadened line shapes of the rovibrational transitions of the (v_1 + 3v_3) combination-overtone band of C_2H_2 have been studied by using a near IR diode laser spectrometer. The 2f frequency detection technique has been employed for signal detection of these weak band transitions. The linestrength parameters and broadening coefficients (HWHM) have been extracted by fitting the observed line shapes with Voigt profiles. Helium, lightest noble gas perturber, exhibits the effect of close collisional dephasing on pressure broadened line profiles. Due to overlapping of atomic orbitals the repulsive interaction dominates over attractive interaction for collision diameter in the 3 to 4 A range. In order to interpret this type of linear polyatomic-monatomic collision phenomena the Tipping-Herman potential has been chosen. Emphasis has been given to the analysis of observed data to obtain information about interaction potential, phase-shift and molecular constants. The results obtained from detailed semi-classical model calculations are found to be in good agreement with the observed data.