THE DEPENDENCE OF INTERMOLECULAR INTERACTIONS UPON VALENCE COORDINATE EXCITATION: THE $v_{HF}=4$ LEVELS OF ArHF

Author Institution: Department of Chemistry and Chemical Biology, Harvard UniversityThe valence slate dependence of the Ar - HF interaction potential is extended to $v_{HF} = 4$. Three new $ArHF (v_{HF} = 4)$ states, (4000), (4100), and (4110), are observed between 14780 and $14880 cm^{-1}$ using intracavity laser induced fluorescence. The spectroscopic constants of these states are: (4000) $v_{o} = 14783.60323(30) cm^{-1}$, and $B = 0.1036068(68) cm^{-1}$; (4100) $v_{o}= 14867.41906(70) cm^{-1}$, $B =0.102612(27) cm^{-1}$; and $(4110) \nu_{o} = 14875.04673(31) cm^{-1}$, $B = 0.1012823(73) cm^{-1}$ respectively. In conjunction with the previous ArHF results $(v_{HF}=0-3)$, the spectral red shifts of ArHF (v000) increase more rapidly than linearly, from $9.654 cm^{-1}$ at v=1 to $48.024 cm^{-1}$ at v=4. The rotational constants of $ArHF(v000)$ increase essentially linearly, with $v_{HF}$, noticeably increased by 1.30% (40 MHz) at v=4. The classical turning point of HF is extended by $0.4 {\AA}$ from $r_{e}$ at v=4, showing no evidence for Ar-H repulsion. The spectral red shift for linear hydrogen bonded Ar-HF (v000) indicates a strong enhancement of binding energy upon HF valence bond elongation, while the rotational constant indicate an almost surprising decrease in heavy atom separation. Both the T-shaped ArHF (v 110) and anti-linear Ar-FH(v100), however, show very little dependence of binding energy upon $v_{HF}$ valence excitation. These observations are in good accord with the ab initio calculations of the Ar-HF intermolecular potential surface