Electronic transitions from the A 2Πu i(v=3) level of N+2 induced by inelastic collisions with helium atoms

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Abstract
An optical–optical double-resonance technique utilizing two pulsed lasers is used to study collision-induced electronic transitions from the N+2 A 2Πui(v=3) level by helium. Collisional deactivation paths are determined by this technique and found to be between this level and the X 2Σ+g (v=7 and 6) levels. The same propensity for ΔJ≊0 occurs for both of these paths in spite of an electronic energy gap size of approximately 0 cm−1 between the A(v=3) and X(v=7) levels and a large gap size of about 1950 cm−1 between the A(v=3) and X(v=6) levels. The electronic quenching rate from A(v=3) to X(v=7) is found to be only about three times larger than that to the X(v=6) level. We use this branching ratio in an electronic relaxation model to determine the collisional quenching rates between the A(v=3) and X(v=7 and 6) levels. These state specific rates are determined by fitting the model to observed radiative decay curves from the A(v=3) level obtained at various helium pressures. There is excellent agreement between the analytical and observed decay curves. The relatively efficient nature of the collision-induced electronic transition over the large energy gap is somewhat surprising in view of the fact that the nitrogen ions and helium atoms must remove most of this energy as translational kinetic energy. We have also revised our previous rate constants from the A 2Πui(v=4) level for 14N+2 and 15N+2.