Magnetic and microwave field effects for single rotational levels of the 0(0)(0)-band of oxalylfluoride in cooled jet conditions

Fluorescence intensity and decay in oxalylfluoride vapors ((COF)(2)), excit ed to single rotational levels (SRLs) of the (1) A(u)(0(0)) state of the (A ) over tilde (1)A(u)<--(A) over tilde (1)A(g) transition, were measured as a function of an external magnetic field. On excitation to these levels, dy namics in zero field may be described in the small-molecule limit, with flu orescence exhibiting an almost exponential decay. However, at increased fie ld strength B the initial fluorescence decay becomes faster, the decay prof ile becoming biexponential at higher fields. Thus, a magnetic field-induced change of dynamics occurs in the (A) over tilde (1)A(u) state, from that o f a small molecule, to the intermediate case. The decay rate constant of th e fast component was measured for different SRLs, being independent on the magnetic field strength, while the slow component lifetime is field depende nt, increasing at higher fields. Both the fast and slow decay lifetimes dep end on the studied SRL. At higher fields, the slow component amplitude decr eases, while that of the fast component increases with subsequent saturatio n at high fields. Halfwidth value (B-1/2) of the field dependence of the sl ow component amplitude increases linearly with (2J(')+1)(-1). Structure of the OD EPR spectrum of (COF)(2) excited to the J(')=4 level was resolved. E xperimental data are interpreted using the indirect mechanism theory in the low level density limit. (C) 1999 American Institute of Physics. [S0021-96 06(99)00137-3].