THE MYSTERY OF THE CO DIMER - ASSIGNMENTS FROM VARIABLE-TEMPERATURE JET-COOLED INFRARED-SPECTRA

The infrared absorption spectrum of the CO dimer was studied in the vi cinity of the CO fundamental band in both axisymmetric and planar supe rsonic jet expansions. By probing the jet at varying distances downstr eam, we observed (CO)(2) spectra over a range of effective rotational temperatures from about 15 down to 1 K. The temperature dependence of the transitions enabled us to identify one perpendicular and two paral lel subbands arising from the lowest rotational levels of the dimer. T he effective intermolecular separation for (CO)(2) was determined to b e about 4.35 Angstrom. The only previous assignment of CO dimer spectr a is incompatible with our results. (C) 1998 Elsevier Science B.V. All rights reserved.