15min:

CHENG-CHI CHUANG AND WILLIAM KLEMPERER, Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138.

The valence state 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) ₀ = 14783.60323(30) cm^-1, and B = 0.1036068(68) cm^-1; (4100) ₀ = 14867.41906(70) cm^-1, B = 0.102612(27) cm^-1; and (4110) ₀ =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 Å ~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(v110) 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.

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