Low-Temperature Rotational Relaxation of CO in Self-Collisions and in Collisions with Ne and He

G. A. AMARAL; F. J. AOIZ; L. BAÑARES; J. BARR; V. J. HERRERO; B. MARTÍNEZ-HAYA; M. MENÉNDEZ; G. A. PINO; I. TANARRO; I. TORRES; J. E. VERDASCO

JOURNAL OF PHYSICAL CHEMISTRY A

American Chemical Society

Lugar: Georgia - USA; Año: 2005 vol. 109 p. 9402 - 9413

1089-5639

The low-temperature rotational relaxation of CO in self-collisions and in collisions with the rare-gas atoms Ne and He has been investigated in supersonic expansions with a combination of resonance-enhanced multiphoton ionization (REMPI) spectroscopy and time-of-flight techniques. For the REMPI detection of CO, a novel 2 + 1¢ scheme has been employed through the A1¦ state of CO. From the measured data, average cross sections for rotational relaxation have been derived as a function of temperature in the range 5-100 K. For CO-Ne and CO-He, the relaxation cross sections grow, respectively, from values of  20 and 7 Å2 at 100 K to values of  65-70 and 20 Å2 in the 5-20 K temperature range. The cross section for the relaxation of CO-CO grows from a value close to 40 Å2 at 100 K to a maximum of 60 Å2 at 20 K and then decreases again to 40 Å2 at 5 K. These results are qualitatively similar to those obtained previously with the same technique for N2-N2, N2-Ne, and N2-He collisions, although in the low-temperature range (T < 20 K) the CO relaxation cross sections are significantly larger than those for N2. Some discrepancies have been found between the present relaxation cross sections for CO-CO and CO-He and the values derived from electron-induced fluorescence experiments.