Broadening, shifting, and line mixing in the 0310 ← 0110 parallel Q branch of N2O

Abstract The 03 1 0 ← 01 1 0 parallel Q branch of N 2 O has been studied at 297 K and over the pressure range 1–130 torr. Absorption spectra were recorded using a high resolution (1.5 MHz or 5 × 10 −5  cm −1 ) and high signal-to-noise (>3500:1) mid-infrared spectrometer based on difference-frequency infrared generation in AgGaS 2 . In the low-pressure range (1–11 torr) we obtained accurate values for the line strengths, the broadening coefficients, the weak mixing coefficients, and the overall shifting of the branch. The medium pressure results, ranging from 23 to 130 torr, were analyzed by treating the band as a whole, using a relaxation matrix formalism, based on an energy gap scaling law. We find, effectively, that only 36% of the rotationally inelastic collisions are associated with Q branch mixing, the rest presumably being associated with Q – P and Q – R mixing in the same vibrational band. The pressure shifting coefficient of the 03 1 0 ← 01 1 0 Q branch as a whole was also determined and found to be 5.8 × 10 −3  cm −1 /atm towards lower frequencies.