RADIATIVE LIFETIMES AND REACTIVITY OF METASTABLE NO+(A3-SIGMA+,V) AND O2+(A4-PI-U,V)

The radiative lifetimes and reactivity of metastable NO+ (a 3-SIGMA+) and O2+ (a 4-PI-(u)) have been investigated using a triple cell ion cyclotron resonance (ICR) spectrometer. Radiative lifetimes of (100 +/- 20) ms and (135 +/- 25) ms have been found for NO+ (a 3-SIGMA+) v greater-than-or-equal-to 1 and v greater-than-or-equal-to 0 respectively, with Ar and CO2 as monitor gases. The overall reaction rate of NO+ (a 3-SIGMA+, v greater-than-or-equal-to 1) with Ar (6.5 x 10(-10) cm3 s-1) is 1 order of magnitude larger than the rate of v = 0 determined in flowing afterglows. CO2 reacts at collision rate. For O2+ the overall lifetime of v greater-than-or-equal-to 0, determined with Ar as monitor, is (30 +/- 6) ms in between the two values (7 and 130 ms) found by Bustamente et al. using the photodissociation technique. The possible reasons for the longer lifetimes determined in previous ICR experiments is discussed. In the absence of any ab initio calculation, the experimental results on NO+ (a 3-SIGMA+) may only be compared to values calculated using an approximated perturbation model. Unfortunately, the reliability of this model, also used in the previous studies, is very limited because of the large uncertainty on the coupling between the metastable a 3-SIGMA+ and the perturbing radiative A 1-PI states.