Author : Mohammed T. Hussein and Anas Kahtan Mostfaa

IR and Raman spectra of BP vibrational properties are investigated using density functional theory at the PBE/6-31G(d) level and basis including polarization functions. The frequencies in the vibrational spectrum are analyzed against reduced masses, force constants and intensities of vibration. An analysis of vibrational modes, in terms of reduced masses, force constants and IR intensity, was then performed. The size-related change of certain vibrational frequencies of BP diamondoids was compared with the experimental bulk. The spectrum can be divided into two regions depending on the properties of the vibrations or the gap separating them. In the first region, results show good matching to several experimentally obtained lines. The 500 cm−1 broad-peak region is characterized by pure B–P vibrations. In the second region the matching also extends to B–H,P-H vibration frequencies that include different modes such as symmetric, asymmetric, wagging, scissor, rocking and twisting modes. Radial breathing mode frequency began from 550 cm−1 for the smallest molecule BPH6 and decreased with fluctuations. Longitudinal optical mode began from 500 cm−1 for the smallest molecule and increased with fluctuations, heading to800 cm−1 (24 THz) as its bulk limit.

Keywords: BP, infrared spectroscopy, DFT

Article published in International Journal of Current Engineering and Technology, Vol.6, No.3 (Sept-2016)