Rotational-RKR inversion of intermolecular stretching potentials: Extension to linear hydrogen bonded complexes

Abstract

A Rydberg–Klein–Rees (RKR)-based method is described which determines effective 1D intermolecular stretching potentials for polyatomic linear complexes from high precision rotational data alone. This extends the ‘‘rotational RKR’’ inversion method from pseudodiatomic van der Waals clusters with only two nonhydrogenic atoms to much larger complexes with several heavy atoms. Sample inversion of rotational eigenvalues generated from a model 1D potential reproduces the model potential to ≲0.13 cm−1 accuracy and correctly predicts harmonic frequencies, force constants, and dissociation energies to ≲0.1%. In contrast, the commonly used ‘‘pseudodiatomic’’ approximation lead to quite significant (10%–20%) errors, even for exact model potentials for which these approximations were developed. The method is further tested on high resolution near IR spectroscopic data of 14N14N–HF, which determines the vibrationally averaged hydrogen bond stretching potential from 3.39≲Rcm≲3.85 Å. The RKR data yield a hydrogen bond length of RN–H=2.106 Å (2.079 Å) and predict a van der Waals stretching frequency of 86.9 cm−1 (90.7 cm−1) for vHF=0 (vHF=1). RKR fits that incorporate electrostatic models of long-range behavior also permit estimates of the hydrogen bond dissociation energies and vibrational red shift for the vHF=0 and vHF=1 states, respectively. The range of D0 values agree reasonably well with previous ab initio calculations, and the difference in D0 values between vHF=0 and 1 is in good agreement with the experimentally observed red shift.