Vibrational relaxation of NO(=1–3) and NO2(0,0,1) with atmospheric gases

The 248 nm photolysis of NO2/N2O4: Time-resolved Fourier transform infrared emission from NO and NO2, and quenching of NO (v=5–8)

“…Relaxation into and out of vϭ2 will also affect the measured population at 2 s, but these processes are factors of 3 and 2 slower than reaction ͑2͒. 20 The value for vϭ2 extrapolated to zero time in Table II shows error bars ͑Ϯ27%͒ which are larger than the expected contribution of reaction ͑2͒, and we conclude that these errors satisfactorily encompass any possible contribution from the reaction. Cold gas filter experiments were also conducted in order to estimate the nascent population in vϭ1 from the photolysis.…”

“…7 shows, our previously measured values of P/v for vϭ1 -3 at larger ⌬E appear to reach a limiting value, which we have interpreted as arising from complex formation. 20 The magnitudes of the reduced probabilities for quenching of NO(v) by NO 2 ͑Fig. 7͒ appear to be heading towards values close to resonance which are some 50% of those for process ͑4͒.…”

“…Table III shows that the rate constants increase noticeably with vibrational quantum number, continuing the trend previously observed for vϭ1 -3. 20 The data are given in Table III and plotted in Fig. 7 as reduced probabilities P/v, where P is the probability of a gas kinetic collision between NO(v) and NO 2 leading to single quantum loss in NO, as a function of the magnitude of the energy discrepancy ⌬E for the exothermic process ͑3͒.…”

“…27 We have previously argued that the approximate constancy of P/v with ⌬E for vϭ1 -3 provides further evidence that process ͑3͒ is not dominant, as the simple onequantum exchange process would be expected to show values of P/v which drop with increasing energy discrepancy. 20 Instead, a process was invoked in which N 2 O 3 complex formation plays a role, but in which the energy is not fully equilibrated before dissociation ͑full equilibration would imply constant values of P, and statistical redistribution of the available energy rather than single quantum loss in NO͒. Figure 7 shows rising P/v values for vϭ5 -8 and suggests that process ͑3͒ plays a larger role close to resonance.…”

“…Previously, we have reported that slow energy transfer from the vibrationally excited O 2 formed in process ͑2͒ is the major excitation route for NO 2 (0,0,1) for photolysis at 355 and 308 nm, but that at 248 nm the kinetics of the NO 2 (0,0,1) emission changes in a way consistent with an additional contribution from fast, near-resonant energy transfer in process ͑3͒ from the high vibrational levels formed. 20 Here, we report the relative intensities of the emission bands from NO and NO 2 (0,0,1). For photolysis at 308 nm the initial emission signal from nascent NO was four times greater than the peak of the emission from NO 2 , 20 whereas at 248 nm the factor is reduced to 1.5.…”