Musical Molecules: Sonifying the IR Spectra and Modeling Intramolecular Vibrational Energy Redistribution of Small Molecules

This work explores how small molecules sound. Infrared (IR) spectra of HCl, H2O, NH3, and acetone are mapped into the audible range using a simple anharmonic oscillator model and NIST vibrational data. Comparing harmonic and anharmonic sonifications reveals systematic pitch flattening, beating, and the emergence of combination bands, which are analyzed with spectrograms and autocorrelation functions. A time-dependent model of intramolecular vibrational energy redistribution (IVR) in acetone, implemented by "plucking" a single mode, produces evolving sound textures that mirror energy flow through the molecule. These results suggest that sonified IR spectra can provide an intuitive, pedagogical window into anharmonicity, mode coupling, and IVR.