To further investigate the F-19 and H-1 nuclear hyperfine structure and Zeeman effect in the simplest singlet carbene, HCF, we recorded polarization quantum beat spectra (QBS) of the pure bending levels 2(0)(n) with n=0-7 and combination bands 1(0)(1)2(0)(n) with n=1-6 and 2(0)(n)3(0)(1) with n=0-3 in the HCF (A) over tilde (1)A"<--(X) over tilde (1)A' system. The spectra were measured under jet-cooled conditions using a pulsed discharge source, both at zero field and under application of a weak magnetic field (<30 G). Analysis yielded the nuclear spin-rotation constants C-aa and weak field Lande g(aa) factors. Consistent with a two-state model, the majority of observed vibrational levels exhibit a linear correlation of C-aa and g(aa), and our analysis yielded effective (<(a)over tilde>) hyperfine constants for the F-19 and H-1 nuclei (in MHz) of 728(23) and 55(2), respectively. The latter was determined here owing to the high resolving power of QBS. The vibrational state selectivity of the F-19 hyperfine constants is discussed, and we suggest that the underlying Renner-Teller interaction may play an important role. (C) 2004 American Institute of Physics.