The NO(a 4Π) state: Collisional removal of v=11 and a 4Π–B 2Π interactions

Abstract

State-resolved collisional energy transfer in highly excited NO 2 . I. Cross sections and propensities for J, K, and m J changing collisions Vibrationally excited levels of the a 4 ⌸ state, the lowest electronically excited state of the NO molecule, can be studied through their collisional energy transfer to the radiating B 2 ⌸ state. Following one-photon excitation in the 11-0 band of the forbidden a 4 ⌸ -X 2 ⌸ transition with the output of a tunable dye laser, we monitor the temporal evolution of the emission from the vϭ2 level of the B 2 ⌸ state. From pressure-dependence analysis, we determine the removal rate coefficients for a 4 ⌸(vϭ11) with NO, O 2 , N 2 O, N 2 , CO 2 , He, and Ar. In addition, using direct B 2 ⌸ excitation of the vϭ2, 3, 4 levels, we obtain removal rate coefficients for the same colliders. These vibrational levels span the region around a 4 ⌸(vϭ11). In general, a 4 ⌸ removal is quite fast, ranging from rate coefficients of 1.0ϫ10 Ϫ12 cm 3 s Ϫ1 to more than 1.0ϫ10 Ϫ10 cm 3 s Ϫ1 , and is substantially faster than B 2 ⌸ removal for N 2 , N 2 O, CO 2 , and Ar. NO͑B 2 ⌸, vϭ3͒ removal is generally much faster than that for the vϭ2 and vϭ4 levels, because of a localized perturbation between the vϭ12 level of the a 4 ⌸ state and vϭ3 of the B 2 ⌸ state. Preliminary measurements on transfer between the b 4 ⌺ Ϫ and B 2 ⌸ states are reported.

Sensitive detection of metastable NO and N2 by reactive collisions with laser-excited Li

“…By using laser excitation instead of an electrical discharge to populate the a 4 Π i state from the X 2 Π r ground state, it will be possible to selectively excite specific vibrational states in NO(a 4 Π i ) [39,42,43]. Such a state preparation scheme will allow for the detailed study of vibrational-state-selected NO(a 4 Π i )-Li(2 2 P 3/2 ) collisional autoionization and-in combination with a sensitive fluorescence detector-its competition with intramolecular collisional energy transfer.…”

Time-resolved observations of vibrationally excited NO X 2Π (v′) formed from collisional quenching of NO A 2Σ+ (v = 0) by NO X 2Π: evidence for the participation of the NO a 4Π state

“…2 The former method has been used to determine collisional removal rates of NO a 4 Π (v = 11) with NO, O2, N2O, N2, CO2, He and Ar. [9][10][11] The reverse processes (removal of the approximately energetically equivalent vibrational levels of the B state) have also been reported, with the conclusion that these processes are fast, with rate constants ranging from 10 -12 to 10 -10 cm 3 molecule -1 s -1 . 10,11 One measurement has been reported which is pertinent to levels below v = 11: Ottinger and Shen 12 used a molecular beam technique to form vibrationally excited NO a 4 Π, collided it with ground state NO and observed γ band emission resulting from formation of NO A 2 Σ + in the process:…”

“…1,2,7,8 Despite the importance of the a 4 Π state, very little is known about its gas-phase kinetic behaviour, largely because of the difficulty in preparing and detecting it in a sensitive quantum stateresolved fashion. Direct excitation in the spin forbidden (and weak) a -X transition has been achieved for high vibrational levels (v = 11 -15), where the Franck Condon factors maximise, with detection being either through emission from the gateway levels in the B state [8][9][10] or by surface ionisation of the metastable a 4 Π state produced in a molecular beam. 2 The former method has been used to determine collisional removal rates of NO a 4 Π (v = 11) with NO, O2, N2O, N2, CO2, He and Ar.…”

Rate Parameters for Electronic Excitation of Diatomic Molecules: NO Radiation

“…4, interaction potentials of NO electronic states are constructed in this work from the known spectroscopic constants [4,13], but those of the NO a 4 r and b 4 states are taken from the works of Scheingraber and Vidal [26] and Gadd and Slanger [33]. The energy level of the C 2 r v 0 is located very close to the dissociation limit [26,28,[31][32][33]35,37,38] of the X 2 r . The a 4 state crosses the C 2 r state at a point slightly above the C 2 r v 0 level.…”