The radiative lifetimes of O +2(a 4Π u, v) and NO +(a 3∑ +, v) revisited

Abstract

The spin-forbidden radiative decays of metastable O + 2(a 4Π u, v) and NO +(a 3∑ +, v) have been reinvestigated using our recently improved tirple cell FT-ICR spectrometer. The monitor ion technique was used to probe the first excited state of O + 2(a 4Π u) and NO +(a 3∑ +). A radiative lifetime of (55 ± 7) ms has been found for O 2 +(a 4Π u) with Ar and CO 2 as monitor gases. For NO +(a 3∑ +) we found (680 +91 −87) ms with CO 2 (proving v ⩾ 0) and (516 −62 +65) ms with Ar (probing v ⩾ 1) respectively as monitor gases. For such long lifetimes it is mandatory 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 gas pressure and rate constants have been carefully determined. For O + 2, a double exponential decay due to the metastable state and to high vibrational levels of the ground state has been observed. As a consequence the experimental lifetimes depend on the observation time window explaining most of the differences with the previous published results. For NO +(a 3∑ +) the present lifetime is in good agreement with the results of Kuo. [C.H. Kuo, T. Wyttenbach, C.G. Beggs, P.R. Kemper and M.T. Bowers, J. Chem. Phys., 92 (1990) 4849] and with the recent theoretical calculations.