Spectroscopic Features of Weak Intermolecular Interactions: IR Spectrum of the Formamide–Water Complex Revisited

This work provides reference data on the vibrational spectrum of formamide and its modification upon complexation with one water molecule, relevant for the interpretation of complex spectral patterns observed in interstellar ices both in the laboratory experiment and with the James Webb Space Telescope. To this end, new measurements of the formamide and formamide-water vibrational spectra have been performed using low-temperature argon matrix isolation fourier transform infrared (MI-FTIR) spectroscopy. Analysis and interpretation of experimental spectra have been supported by fully anharmonic vibrational second-order perturbation theory computations, which allowed the assignment of additional nonfundamental bands of formamide as well as for unveiling an elusive formamide-water structure. This intermolecular complex, characterized by an O···H-O hydrogen bond, had not been identified in prior MI-FTIR studies, although it was observed in the gas phase.