The dependence of intermolecular interactions upon valence coordinate excitation:: The υHF=4 levels of ArHF

The valence state dependence of the Ar-HF interaction potential is extended to upsilon(HF)=4. Three new ArHF (upsilon(HF)=4) states, (4000), (4100), and (4110), are observed between 14 780 and 14 880 cm(-1) using intracavity laser induced fluorescence. The term values and rotational constants of these states are the following: (4000) nu(0)=14 783.603 23(30) cm(-1), B=0.103 606 8(68) cm(-1); (4100) nu(0)=14 867.419 06(70) cm(-1), B=0.102 612(27) cm(-1); and (4110) nu(0)=14 875.048 30(39) cm(-1), B=0.103 217(19) cm(-1), respectively. The spectral red shifts of ArHF (upsilon 000) dramatically increase from 9.654 cm(-1) at upsilon=1 to 48.024 cm(-1) at upsilon=4. The rotational constant of ArHF(4000) increases essentially linearly with HF valence excitation, becoming 1.3% (40 MHz) greater than that observed at upsilon=0. At upsilon=4, the outer classical turning point of HF is extended by 0.4 Angstrom from r(e), and there is no evidence for Ar-H repulsion. The spectral red shift for linear hydrogen bonded Ar-HF(upsilon 000) indicates a strong enhancement of binding energy upon HF valence bond excitation, while the rotational constant reveals an almost surprising decrease in heavy atom separation. Both the T-shaped ArHF(upsilon 110) and antilinear Ar-FH(upsilon 100), however, show very little dependence of binding energy upon upsilon(HF) valence excitation. These observations are in good accord with the ab initio intermolecular potential surface. (C) 2000 American Institute of Physics. [S0021-9606(00)00134-3].