Phase shift cavity ring down and FT-VIS measurements of C–H (Δv = 5) vibrational overtone absorptions

The integrated absorption bands for the C–H stretching overtones (Δv = 5) of C2H4, C2H6, C3H8, C4H10, HC(CH3)3, and C(CH3)4 have been measured at 295 K between 13 000 and 14 300 cm−1, using the phase shift cavity ring down (PS-CRD) technique. Similar absorption bands have been obtained using a White cell with an optical path length of 6.0 m and a Fourier transform spectrophotometer operating in the visible (FT-VIS) region. The integrated intensity and the linearity of the absorption with the density of the gas are independent of the form of modulation of the laser (square or sine wave) using the PS-CRD technique. The oscillator strengths calculated with the two techniques are in excellent agreement.