Electronic quenching, rotational relaxation, and radiative lifetime of NH(A 3Π, v′=0, N′)

Abstract

Using ArF (193 nm) laser photolysis of NH₃, excited triplet NH(A ³Π, v’=0, N’) radicals were generated with a hot rotational distribution (N’_max=8–13). From the decays of the excited radicals, the average lifetime for this rotational distribution was determined to be 465±14 (3σ) ns. The values of the rate constants for the electronic quenching by NH₃, NO, CH₄, H₂, CO, Xe, O₂, CO₂, Ar, N₂, and He were found to decrease in the given order. Rotational relaxation was found to be so efficient to compete with the electronic quenching. The electronic quenching of rotationally relaxed NH(A ³Π, v’=0, T_rot=300 K) by NH₃ and H₂ was observed to be 1.6 and 1.5 times faster than that of the unrelaxed system. The trend in the rate data can be described by Parmenter’s correlation for most molecules studied, hence indicating attractive forces being effective during the quenching process.