The spectrum of the dimer (NO)2 in the gas phase has been studied in the near infrared at temperatures between 118 and 138 K. More specifically, the measure of absorption intensity of the ν4 and ν1 + ν4 bands has yielded the heat of formation of the dimer, −2.25 kcal/mol at 128 K, and revealed the influence of the low vibrational modes on this measure. The observation of the ν4 – ν6, difference band has yielded the wave number value of the ν6, fundamental band, forbidden in the infrared. The rotational constants of the vibrationally excited state were found to be larger than the ground state rotational constants, this result being very unusual.

The collision-induced absorption fundamental band of N(2) has been investigated in the 2100-2600 cm(-1) spectral region. Laboratory measurements have been undertaken over the temperature range 193-297 K. Binary-absorption coefficients for N(2) absorption induced by collisions with N(2) and O(2) are reported and compared with N(2) temperature-dependent continua from atmospheric measurements.

The absorption beyond the ν3-band head of CO2 broadened by argon has been measured at room temperature. The absorption exhibits a strong sub-Lorentzian behavior (several orders of magnitude) resulting from collisionally induced line interferences which transfer intensity from this wing region to the ν3-band center. This wing absorption region implies detuning frequencies from resonances much larger than the reciprocal duration of collision. Consequently, finite duration of collisions in rotational energy transfers and initial correlations must be included in absorption calculation. A line-by-line coupling theory accounting for both these effects has been recently proposed [J. Chem. Phys. 89, 625 (1988)] and is applied here to a detailed study of the CO2–Ar collisional system. A convenient generalized detailed balance correction is introduced in this theory to overcome the limitation of the assumed resonant character of the energy transfer in the short time limit with respect to the thermal time ( βℏ)−1. The calculated absorption is in quantitative agreement with experiment. The origin and the nature of the empirical correcting factor currently used in similar studies are clearly established on a firm physical basis.