Electronic spectroscopy of polyatomic molecules probed using VUV synchrotron radiation

Electronically excited states of molecules are of fundamental importance in the understanding of radiative and non-radiative processes in many diverse areas like atmospheric physics and chemistry, astrophysics, pollution control, etc. It is well recognized that photochemical processes in the upper atmosphere proceed through formation of highly excited and super-excited states. Investigation of the excited state electronic structure of polyatomic molecules is thus an important field of study, both from the fundamental and applied point of view. VUV/UV photoabsorption spectroscopy of a few environmentally important polyatomic molecules in gas phase using synchrotron radiation is presented. The molecules chosen are the dihalomethanes (CH2X2 and CD2X2, X=Cl, Br, I), dimethyl sulphoxide (DMSO and DMSO-d6) and nitrous oxide (N2O). These studies are motivated by the fact that these molecules are known to play major roles in atmospheric chemistry and consequently the knowledge of their excited state electronic structures is important in the understanding of complex photochemical processes involving them. Interpretation of the observed photoabsorption spectra in terms of the valence, Rydberg and mixed type transitions and vibrational structures accompanying them is done with the help of quantum chemical calculations using the density functional theory (DFT) and the time-dependent DFT.