The spectroscopy and molecular dynamics of the high frequency ν¹₆ intermolecular vibrations in HCN‐‐‐HF and DCN‐‐‐DF

Gas phase rovibrational analysis of the high frequency intermolecular hydrogen bonded bending overtone 2ν⁰₆ [ν₀=1132.4783(2) cm⁻¹] in HCN‐‐‐HF and its corresponding perdeuterated fundamental ν¹₆ [ν₀=409.1660(2) cm⁻¹] are reported. Evaluated rovibrational parameters provide the basis for quantitative modeling of the molecular dynamics associated with this vibration. A quantum mechanical calculation permits determination of the quadratic and quartic force constants K₆₆=537(17) and K₆₆₆₆=4.98(12) cm⁻¹ which in turn are used to estimate the pertinent cubic band stretching interaction constants K₄₆₆=−149.3(50) cm⁻¹ and account for the unexpected behavior in the rotational constant B¹₆. Second order expansion of the vibrational term energies, give X₄₆=−21.61(2), X₆₇=−7.694(1), X₆₆=−14.84(90), g₆₆=−31.04(90) cm⁻¹, neglecting corrections for Fermi resonance. The common isotopic species equilibrium rotational constant B_e is evaluated to be 3681.1(11) MHz.