Buffer-gas pressure broadening for the 2ν ₃ band of methane measured with continuous-wave cavity ring-down spectroscopy

Buffer-gas pressure broadening for the P(1), Q(1), R(0) and R(1) transitions in the 2ν ₃ band of CH₄ was investigated in the 1660 nm region. The pressure broadening coefficients, γ(gas), were determined for a variety of buffer gases: N₂, O₂, He, Ne, Ar, Kr and Xe. The γ values generally increased with increasing polarizability of the buffer gases. γ(air) are 0.056(2) for P(1), 0.056(1) for R(0), 0.061(1) for R(1) and 0.059(1) for Q(1) in units of cm ^-1atm^-1 where numbers in parentheses are one standard deviation in units of the last digits quoted. The temperature dependent parameter (broadening exponent) for air is 0.84(7) for P(1) within the temperature range 233-298 K.