Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

A. Ravi Rau


A series of experimental studies was carried out on diatomic molecules to understand how they interact with intense laser fields. These studies have mainly consisted of multiple photon excitation, ionization and dissociation of hydrogen, oxygen, and chlorine molecules using time of flight electron and ion spectroscopy. I took advantage of the similarities and differences in the molecular structure of these molecules in order to investigate whether different molecules interact differently with the applied fields. Clear experimental evidence of molecular Bond Softening as an intensity dependent variation in the vibrational distribution of molecular ions is being reported for the first time in H$\sb2$ and D$\sb2$. The competition between different channels in the above threshold dissociation of molecules had been predicted recently using the dressed molecular states model. My results on these branching ratios are qualitatively consistent with the theoretical predictions. The study on oxygen concentrated mainly on the anomalous intensity dependence of the final state vibrational distribution. I have used a model similar to Smith's model to explain the role intermediate states play in the ionization of oxygen. In a series of arguments, I have shown that this anomalous behavior can be explained as a pure intermediate state interplay in the first approximation. Finally, in the photoelectron spectroscopy of chlorine, I have observed the positive Ponderomotive shifts known for a long time but never directly observed before. Also observed in the spectra is a very low order above threshold ionization process of highly excited atoms. These observations in chlorine suggest an unexplored mechanism of exposing atoms to intense fields without the risk of their ionization in the rising part of the laser pulses.