The far infrared spectrum of naphthalene characterized by high resolution synchrotronFTIR spectroscopy and anharmonic DFT calculations

Abstract

Using synchrotron radiation, we performed the rotationally resolved Fourier transform infrared absorption spectroscopy of three bands of naphthalene C₁₀H₈, namely ν₄₆-0 (centered at 782 cm⁻¹, 12.7 μm), ν₄₇-0 (centered at 474 cm⁻¹, 21 μm), and ν₄₈-0 (centered at 167 cm⁻¹, 60 μm). The intense CH bending out of plane ν₄₆-0 band was recorded under supersonic jet-cooled conditions using a molecular beam (the Jet-AILES apparatus) and the low frequency ν₄₇-0 and ν₄₈-0 bands were measured at room temperature in a long absorption path cell. The simultaneous rotational analysis of these bands permitted us to refine the ground state (GS) and ν₄₆ rotational spectroscopic constants and to provide the first sets of constants for the ν₄₇ and ν₄₈ modes. The experimental rotational constants were then used as reference data to calibrate theoretical models in order to provide new insights into the accuracy of anharmonic calculations. The B97-1 functional associated with the cc-pVTZ and ANO-RCC basis sets gave a consistent set of results, for rotational constants and fundamental frequencies. The data presented here pave the way for the search of naphthalene through its far-infrared spectrum in different objects of the interstellar medium.