Vibrational spectra of tellurophene and of its perdeuterated isotopomer were computed using the DFT-B3LYP functional with the LANL2DZ(d,p) basis set. The frequencies of fundamental and overtone transitions were obtained in vacuum under the harmonic approximation and anharmonic second-order perturbation theory (PT2). On the whole the anharmonic corrections reduce the harmonic wavenumber values, in many cases better reproducing the observed fundamental frequencies. The largest anharmonic effects are found for the C–H and C–D stretching vibrations, characterized by relatively high anharmonic coupling constants (up to ca. 120？cm？1). For the C–H/C–D stretches, the harmonic H→D isotopic frequency red-shifts overestimate the observed data by 47–63？cm？1 (5.9–8.1%), whereas the PT2 computations exhibit significantly better performances, predicting the experimental data within 1–19？cm？1 (0.1–2.4%). 1. Introduction Tellurophene is a five-membered heterocycle (C4H4Te, Figure 1) homologue of the furan molecule. Tellurophene-based compounds have received great attention for the development and fabrication of promising polymeric conductors [1, 2] and nonlinear optical materials [3–8]. The experimental structure of C4H4Te is available from microwave measurements [9], whereas the infrared and Raman spectra of C4H4Te and of its perdeuterated isotopomer (C4D4Te) were recorded in various phases [10–14]. On the theoretical side, the vibrational spectra of C4H4Te were previously calculated in vacuum under the harmonic approximation by using Hartree-Fock [7] and Density Functional Theory (DFT) computations [15]. However, as well-known in the literature, the harmonic treatment often overestimates experimental wavenumbers of fundamentals and overtones, in particular, of the highest-energy spectral regions [16]. To partially circumvent this deficiency, harmonic frequencies can be corrected through scaling procedures [17, 18] or direct anharmonic calculations [19–21]. Anharmonic terms are usually calculated by means of variational [19] or perturbative [20, 21] treatments. As established in the literature [22], the perturbative methods are less accurate than the variational ones. Nevertheless, many recent results attest satisfactory performances of the perturbative methodologies, especially for the prediction of anharmonic contributions to fundamentals and overtones of cyclic compounds [22–30]. Figure 1: B3LYP/LANL2DZ(d,p) geometrical parameters ( structure) of tellurophene. The data reported in the round brackets refer to the B3LYP/LANL2DZ(d,p) vibrationally averaged geometry (
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