THE RADIATIVE LIFETIMES OF O-2(-PI-U, UPSILON) AND NO+ (A3-SIGMA+, UPSILON) REVISITED() (A4)

The spin-forbidden radiative decays of metastable O2+ (a 4PI(u), upsil on) and NO+ (a 3SIGMA+, upsilon) have been reinvestigated using our re cently improved triple cell FT-ICR spectrometer. The monitor ion techn ique was used to probe the first excited state of O2+ (a 4PI(u) and NO + (a 3SIGMA+). A radiative lifetime of (55 +/- 7) ms has been found fo r O2+(a 4PI(u)) with Ar and CO2 as monitor gases. For NO+(a 3SIGMA+) w e found (680(-87)+91) ms with CO2 (probing v greater-than-or-equal-to 0) and (516(-62)+65) ms with Ar (probing v greater-than-or-equal-to 1) respectively as monitor gases. For such long lifetimes it is mandator y to take into account collisional deactivation processes occurring in the relaxation cell even for pressures below 10(-8) Torr. In order to correct the observed lifetimes, background ps pressure and rate const ants have been carefully determined. For O2+, a double exponential dec ay due to the metastable state and to high vibrational levels of the g round state has been observed. As a consequence the experimental lifet imes depend on the observation time window explaining most of the diff erences with the previous published results. For NO+(a 3SIGMA+) the pr esent lifetime is in good agreement with the results of Kuo et al. [C. H. Kuo, T. Wyttenbach, C.G. Beggs, P.R. Kemper and M.T. Bowers, J. Che m. Phys., 92 (1990) 4849] and with the recent theoretical calculations .