Polarization quantum beat spectroscopy of HCF(Ã ¹ A″). I. ¹⁹F and ¹H hyperfine structure and Zeeman effect

To further investigate the ¹⁹F and ¹H 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 ¹2 ₀ ⁿ with n= 1-6 and 2 ₀ ⁿ3 ₀ ¹ with n= 0-3 in the HCF Ã ¹A″ ← X̃ ¹A′ 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 (ã) hyperfine constants for the ¹⁹F and ¹H 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 ¹⁹F hyperfine constants is discussed, and we suggest that the underlying Renner-Teller interaction may play an important role.