Far Infrared spectrum of naphthalene in the 5-15 THz range: Experimental and theoretical study

The Fourier Transform Infrared technique was employed to measure the terahertz spectrum of naphthalene at room temperature. Naphthalene exhibited six absorption bands in the 5-15 THz range, two of which have not been previously reported. The additional bands appeared at 5.80 and 6.37 THz. Density Functional Theory modeling with PBE0 and TPSSh functionals gave vibrational modes which matched well with the experimental bands despite the slight shifts in energies. The TPSSh functional was found to perform slightly better than the PBEO functional. Comparison of the naphthalene spectrum with the spectrum of terra preta suggested the existence of cyclic hydrocarbons in terra preta.