Quenching of Excited Mercury Atoms(63P1 and 63P0) in Molecular Collisions

The lifetime of Hg(63P0) in a gaseous mixture of Ar and N2 with quenching molecules (Q) was measured by monitoring the decay of the Hg(63P0) concentration following the excitation of Hg by pulsed 253.7 nm radiation. The lifetime in the absence of Q was reduced with the increase in the N2 pressure, being inversely proportional to the total pressure. This can be attributed to the deactivation by impurities involved in the gas and that by collision on the wall of the reaction cell. Deactivation due to impurities is dominant at a total pressure higher than 50 Torr. With quenchers in the mixture, the lifetime measurement gave the quenching cross-section of Hg(63P0). In addition, the measurement of the stationary concentration of Hg(63P0) made it possible to determine the rate for each of the processes 63P1→63P0 and 63P1→61S0. Based on the observed ratio, α=σ2(63P1→61S0)/σ2(63P1→61S0), quenching molecules are classified into three groups. The first group consists of N2O, O2, C2H4, C3H6, and C2H2 with α1.2 These molecules deactivate Hg(63P) to form their triplet states. The second group (CO, NO, H2, C3H8, i-,n-C4H10, and C(CH3)4) in which α≈4 makes the quenching via a short-lived complex (Hg–Q)*. The last group (CH4 and C2H6) has a value of α larger than 100. This is caused by a weak interaction between potential surfaces of Hg(63P)+Q and Hg(61S)+Q.