This thesis consists of two main parts. In the first part the Valence photoelectron spectra of some important biological molecules (two amino acids and three purines) were studied theoretically and experimentally. A new method called Symmetry Adopted Coupled Cluster-Configuration Interaction (SAC-CI) was used to calculate the position and intensity of ionization lines, up to about 20 eV binding energies. A very good agreement between theory and experiment was observed. In the second part, a new method of atomic spectroscopy in the field of optogalvanic spectroscopy is introduced for getting more resolved optogalvanic (OG) spectra. The time domain of optogalvanic signal was considered as an extra dimension for the analysis of the optogalvanic spectra. A time window with a given delay was used to integrate over the different time regions of the temporal OG signals for each wavelength. This method enhanced the resolution of spectra considerably so that very closed transitions, which differ only by few picometers were precisely separated.
