Abstract
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%).
Highlights
Tellurophene is a five-membered heterocycle (C4 H4 Te,Figure 1) homologue of the furan molecule
The vibrational spectra of C4 H4 Te were previously calculated in vacuum under the harmonic approximation by using
The vibrational wavenumbers of C4 H4 Te and C4 D4 Te were determined at the B3LYP/LANL2DZ(d,p) level under the harmonic approximation through analytical computations
Summary
Figure 1) homologue of the furan molecule. Tellurophenebased compounds have received great attention for the development and fabrication of promising polymeric conductors [1, 2] and nonlinear optical materials [3,4,5,6,7,8]. 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 [19,20,21]. In this work we investigate the effects of the anharmonic corrections on the vibrational wavenumbers of fundamental and overtone transitions of C4 H4 Te and C4 D4 Te. The anharmonic terms were predicted in the gas phase using the second-order perturbation theory (PT2) as described in detail by Barone [20]. The Φijk and Φijkl values are obtained through a finite difference scheme using quadratic normal coordinate force constants (Φij ) calculated analytically and performing displacements along each normal coordinate (δq i ): Te (122.9)
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