Experimental and Theoretical Investigations on Electronic Spectra

Polycyclic aromatic hydrocarbons (PAHs) are of great interest to physicists, chemists biologists and environmentalists. Some of these hydrocarbons are carcinogenic and are found in the atmospheric environment. Large PAHs have also been identified in the interstellar matter where they occur in their ionised form. The thesis deals with a detailed study of the electronic spectra of tetracyclic aromatic hydrocarbons, viz. tetracene, pyrene, triphenylene, 1,2-benzanthrane, chrysene and 3,4-benzphenanthrene. The radical cations of these hydrocarbons are produced by UV irradiation of the hydrocarbon-doped boric acid glass. In this process, the hydrocarbon is ionised due to photo-ejection of an electron from the hydrocarbon and gets trapped in the boric acid matrix. Electronic absorption spectra of the hydrocarbon radical cations are measured and the observed results are analysed on the basis of open-shell SCF-CI molecular orbital calculations. An interesting correlation study of the variation of the observed electronic band energies of these molecular ionic systems is made, which shows a definite trend in their movement from one system to another.