The interplay of VSCF/VCI calculations and matrix-isolation IR spectroscopy – Mid infrared spectrum of CH3CH2F and CD3CD2F

[Display omitted] •Matrix-isolation simplifies fluoroethane’s IR spectrum by inhibiting its rotation.•Especially the CH stretch region is resolved with unprecedented precision.•Accurate ab initio vibrational structure is provided by VSCF/VCI on a multi-mode PES.•Best results with a PES at CCSD(T)-F12 level of theory including core-correlation.•Intricate assignments (ν1,ν12,ν13) mastered via interplay of theory and experiment. We present the first matrix-isolation infrared (MI-IR) spectra of CH3CH2F and its isotopologue CD3CD2F in Neon and Argon matrix, together with new gas-phase IR spectra. Extensive vibrational self-consistent field and configuration interaction (VSCF/VCI) calculations are performed, based on an ab initio potential energy surface at ae-CCSD(T)-F12a/cc-pCVTZ-F12 level of electronic structure theory. We encounter an excellent agreement between VCI calculated transitions and the experimental MI-IR and gas-phase IR spectra. Mean absolute deviations are scattering between 1 and 4 cm−1. The interplay of accurate vibrational structure calculations and high-resolution infrared experiments enables unprecedented insights in the CH respectively CD stretch region, providing the first rigorous assignment of the energetically very close ν1,ν12 and ν13 fundamental transitions.