Semi-classical analysis of helium broadened acetylene (nu(1)+3 nu(3)) bandtransitions measured by a NIR diode laser spectrometer

Helium-broadened line shapes of the rovibrational transitions of the (v(1) + 3v(3)) combination overtone band of C2H2 have studied 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 line strength parameters and broadening coefficients (HWHM) have been extracted by fitting the observed line shapes with Voigt profiles. Helium, lightest n oble gas perturber. exhibits the effect of close collisional dephasing on p ressure broadened line profiles. Due to ol overlapping of atomic orbitals t he repulsive interaction dominates over attractive interaction for collisio n 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 Ilas been given to the analysis of observed data to o btain information about interaction potential, phase-shift and molecular co nstants. The results obtained from detailed semi-classical model calculatio ns are found to be ill good agreement with the observed data.