Experimental and theoretical study of the collision-induced fundamental absorption spectra of N-2-O-2 and O-2-N-2 pairs

New experimental and theoretical studies of the collision-induced fundament al absorption spectra of N-2-O-2 and O-2-N-2 pairs, where the first molecul e makes the vibrational transition, are presented for a range of temperatur es. Most of the absorption arises from the long-range quadrupolar and hexad ecapolar mechanisms for which accurate matrix elements are available from o ther experimental measurements or from ab initio calculations. As in previo us studies for N-2-N-2 and O-2-O-2, we vary the molecular matrix elements a nd the coefficients of the short-range induced dipole moments within realis tic limits to obtain the best global fit to the temperature-dependent integ rated intensities for all the experimental data. This procedure provides a more stringent test of the theory than the previous studies in which the pa rameters for N-2 and O-2 were optimized independently. Using the parameters thus determined, we then calculate the spectral profiles assuming the line shapes calculated quantum mechanically for N-2. The agreement between theo retical and experimental profiles is good, but discrepancies in the plateau region of the S-branch, which we attribute to metastable dimer effects, an d in the wings of the bands, which we attribute to the neglect of line mixi ng and higher-order induction mechanisms, still remain. (C) 2001 Elsevier S cience Ltd. All rights reserved.