Isotope effects in high-resolution NEXAFS spectra of naphthalene

We investigated the high-resolution near-edge X-ray absorption fine structure of hydrogenated and fully deuterated naphthalene in the gas phase. The rich fine structure in the C K-edge spectra is identified as coupling of the electronic transitions to various vibronic excitations as supported by ab initio calculations. The differences in the spectroscopic signatures of the two isotopes strongly suggest significant contributions of C-H (C-D) and C-C vibrational modes. This is corroborated by a comparison with the similar spectra of (deuterated) benzene, which allows the identification of at least two CH (CD) modes and one CC mode.