A theoretical gas phase study of the molecular structures and vibrational spectra of novel penta-1,4-diyne-3-thioketone and penta-1,4-diyne-3-selenoketone

Molecular parameters, namely bond lengths, bond angles, rotational constants, dipole moments and energies, and vibrational infrared spectra parameters, namely harmonic vibrational frequencies and absolute intensities, of penta-1,4-diyne-3-thioketone and penta-1,4-diyne-3-selenoketone in C2v symmetry are predicted at the ab initio MP2 and DFT levels of theory. The basis set employed for these methods is 6-311++G(d,p) and the functional used for the DFT method is B3LYP. All calculations have been carried out using Gaussian 03W. The molecular parameters and vibrational spectra of penta-1,4-diyne-3-one [Y. Umar, J. Mol. Struct. (THEOCHEM) 728 (2005) 111-115] have been calculated at the same levels of theory and basis set employed in this study and the results obtained are in good agreement with available experimental literature data. Therefore, data from the present theoretical gas phase study are valid for the molecular structures and vibrational spectra of the novel sulfur and selenium analogues of penta-1,4-diyne-3-one and they could be used for the characterisation of these compounds as and when they are synthesised. This work also compares the effect on molecular and vibrational parameters when the oxygen of the carbonyl group of penta-1,4-diyne-3-one is substituted by sulfur and selenium.