EXTERNAL MAGNETIC-FIELD EFFECTS AND ROTATIONAL STATE DEPENDENCE ON FLUORESCENCE OF PYRAZINE-D4

External magnetic field effects on intensity and decay of fluorescence of pyrazine-d4 have been examined with excitation at the individual rotational lines of the 0-0 band belonging to the S0 --> S1 transition. A single exponential decay modulated by the quantum beats or a pseudobiexponential decay of fluorescence observed at zero field with excitation into very low rotational levels changes to a biexponential decay, as the strength of the external magnetic field (H) increases. The intensity of the slow component effectively decreases with increasing H, whereas the intensity of the fast component increases with increasing H, though both intensities reach constant values at high fields, respectively. The field-induced change of the fast component becomes smaller with increasing J', whereas the magnetic quenching of the slow component becomes more efficient with increasing J'. The fluorescence lifetime of the slow component of pyrazine-d4 decreases with increasing H and has a tendency to increase with increasing J' both in the absence and in the presence of H. A field-induced mixing between T1 (n-pi*) and T2 (pi-pi*) is suggested to play a significant role in magnetic field effects on fluorescence of pyrazine-d4.