Knowledge Bank

Between 330 and 400 nm the 2+1 REMPI spectrum of $SiCl3$ exhibits two overlapping vibrational progressions composed of $>30$ members and one vibrational progression composed of 5 members. These band systems, labeled $F~$, $G~$, and $H~$, are tentatively assigned to three distinct Rydberg states that reside between 50100 and $59600cm-1$. The vibrational progressions have an average spacing of $\omega 2=262cm-1$ and are assigned to the $\nu 2$ umbrella modes of the Rydberg states. Electronic origins are not observed. Ab initio calculations on $SiCl3$ and $SiCl3+$ yield geometries and harmonic vibrational frequencies consistent with the spectroscopic assignments and provide the adiabatic ionization potential, $IPa$ = 7.93 $\pm$ 0.05 eV. In combination with a recent experimental value for $\Delta Hf(SiCl3+)$, this leads to $\Delta Hf(SiCl3)=-353\pm 12$ kJ/mol.