Centrifugal distortion in ArHCl

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Abstract
Measurements of centrifugal distortion constants for four isotopic species of the weakly bound, wide amplitude bender ArHCl are reported. Their relationship to an effective radial potential and the associated vibrational wavefunction is discussed. Although the stretching vibrational frequency and the resulting force constant do not have a straight forward relationship to the nonharmonic, angle averaged radial potential, an interpretation of the centrifugal distortion constant in terms of the standard deviation—or width—of the radial wavefunction is proposed. It is shown that a harmonic approximation for the standard deviation of the wavefunction accurately reflects a realistic wavefunction for a complicated potential surface. The derived constants for the four isotopic species are as follows: D0(kHz) ω (cm−1) k (mdyn/Å) σ= (〈R2〉−〈R〉2)1/2(Å) ArH35Cl 20.0(4) 32.4 0.0117 0.166 ArH37Cl 19.0(4) 31.9 0.0114 0.165 ArD35Cl 17.1(4) 34.4 0.0134 0.160 ArD37Cl 16.4(4) 33.7 0.0132 0.159.