Quenching of SO_2 phosphorescence by a magnetic field

摘要

Phosphorescence excitation spectra of the a~3B_1 ← X~1A_1 transition of SO_2 were measured in the absence and presence of a magnetic field (B = 0.44 T, P(SO_2) = 0.7 Torr). The absorption and phosphorescence excitation spectra of the a~3B_1 ← X~1A_1 transition of SO_2 measured in the absence of a magnetic field show that the relative intensity of the bands of the phosphorescence excitation spectrum is smaller than the relative intensity of the corresponding bands of the absorption spectrum beginning with the (0, 2, 0) band. In the presence of a magnetic field, the intensity of the phosphorescence excitation band falls, for ν_(exc) > 26400 cm~(-1). Under the direct excitation of the a~3B_1 ← X~1A_1 transition, the dependence of the magnetic quenching of the SO_2 phosphorescence on the excitation frequency (ν_(exc)) was studied at P(SO_2) = 0.7 Torr and B = 0.44 T. The dependence of the magnetic field effect on ν_(exc) shows that only the vibrationally excited levels of the a~3B_1 state are sensitive to an external magnetic field. The magnetic field strength and the pressure dependence of the magnetic field effects were studied under indirect excitation of the a~3B_1 ← X~1A_1 transition at λ_(exc) = 308 nm. The magnetic field and the pressure dependence were investigated for pure SO_2 and for SO_2 + RH (RH = n-C_5H_(12)) mixtures. It was found that the magnetic field effect was saturated at B ≥ 0.25 T. The saturation value (G_r = l(0.3 T)/l(0)) increases with increasing gas pressure. The magnetic field, the pressure and the excess vibrational energy (ν_(excess)) dependence of the magnetic quenching of SO_2 phosphorescence show that the data observed can be explained by an indirect mechanism within the framework of a low level density approximation.