Collisional coupling and relaxation of N2(B3Πg) and N2 (W 3Δu) vibrational levels in Ar and Ne

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Abstract
Laser excitation from N2(A 3Σ+ u , v=0–6) in Ne and Ar carrier gas in a flowing afterglow apparatus has been used to prepare N2(B 3Π g ) molecules in individual levels from v=3–10. The subsequent N2(B–A) fluorescence intensity was observed to study the coupling and relaxation kinetics of N2(B 3Π g , v=2–10). The decay curves from each level show double (or higher) exponential relaxation. The first component is assigned as primarily the rapid coupling of the N2(B 3Π g ,v) and N2(W 3Δ u , v or v+1) levels, however, the N2 (B′ 3Σ− u , v−4) levels also may be involved for N2(B, v≥5). The slowest decay component represents the subsequent relaxation of the coupled levels. The combination of the two steps is equivalent to apparent stepwise vibrational relaxation of N2 (B 3Π g , v), such relaxation occurs even at low Ar pressures because of the large rate constants and long radiative lifetimes of N2(B) and N2(W). The coupling pattern between N2(B) and N2(W) is analyzed, and rate constants are assigned to elementary steps in the relaxationsequence and the scheme is evaluated. From the analysis of the slow decay components in argon, estimates (20–90 μs) are obtained for the radiative lifetimes for the reservoir levels, which are assigned as N2 (W 3Δ u , v) for N2(B, v≤4) and N2(W 3Δ u , v or v+1) levels plus N2(B′3Σ− u , v−4) levels, for some cases, for N2(B, v≥5).

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