Frequency-normalized Rabi splitting quantifies vibrational strong coupling efficiency in amides and nitriles.

We introduced a normalized descriptor (ℏΩR/ω) that unifies vibrational strong coupling across amide and nitrile vibrational modes through a linear dependence on oscillator strength. Comparison with transfer matrix method simulations revealed molecule-dependent deviations, highlighting the importance of molecular structure and local environments beyond conventional macroscopic models.