Fluorescence intensity and decay in oxalylfluoride vapors ((COF)(2)), excited 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, dynamics in zero field may be described in the small-molecule limit, with fluorescence exhibiting an almost exponential decay. However, at increased field strength B the initial fluorescence decay becomes faster, the decay profile 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 of a small molecule, to the intermediate case. The decay rate constant of the fast component was measured for different SRLs, being independent on the magnetic field strength, while the slow component lifetime is field dependent, increasing at higher fields. Both the fast and slow decay lifetimes depend on the studied SRL. At higher fields, the slow component amplitude decreases, while that of the fast component increases with subsequent saturation at high fields. Halfwidth value (B-1/2) of the field dependence of the slow 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. Experimental data are interpreted using the indirect mechanism theory in the low level density limit.