Pressure broadening coefficients of ν5 fundamental band lines of CH 3I at 7 μm measured by diode laser absorption spectroscopy

Abstract

We have measured the room temperature pressure broadening coefficients, γ, of over 100 lines in five Q-branches of the ν 5 perpendicular band of methyl iodide ( 12CH 3I) using tuneable diode laser absorption spectroscopy. The profiles of individual lines in the PQ 2, PQ 4, PQ 5, PQ 6 and RQ 3 branches were recorded in a 1 m long White cell and at nitrogen or oxygen pressures up to 15 Torr. The lines were fitted to the Voigt profile to obtain the collision broadened line widths. Within individual Q-branches the broadening coefficients decreased monotonically with increasing J and for nitrogen broadening varied between 0.19 cm −1 atm −1 at low J and 0.12 cm −1 atm −1 at high J. The corresponding oxygen broadening coefficients were approximately 20% smaller. Self broadening coefficients were also measured for several of the Q-branches and found to be up to ∼4 times higher than the corresponding nitrogen broadening values.