Photoelectron and Photodissociation Studies of Free Atoms and Molecules, Using Synchrotron Radiation

High resolution synchrotron radiation and Zero -Kinetic-Energy Photoelectron spectroscopy were used to study two-electron transitions in atomic systems at their ionization thresholds. Using this same technique the core -ionized mainline and satellite states of N_2 and CO were studied with vibrational resolution. Vibrationally resolved synchrotron radiation was used to study the dissociation of N_2, C_2H _4, and CH_3Cl near the N 1s and C 1s thresholds. The photoelectron satellites of the argon 3s, krypton 4s and xenon 4d subshells were studied with zero kinetic energy photoelectron spectroscopy at their ionization thresholds. In all of these cases, satellites with lower binding energies are enhanced at their thresholds while those closer to the double ionization threshold are suppressed relative to their intensities at high incident light energies. Zero-Kinetic-Energy photoelectron spectra were taken of N_2 and CO at the N 1s and C 1s ionization thresholds. Vibrational structure was observed for the 1s^{-1} mainlines and the lowest binding energy satellite of CO, which was consistent with the equivalent core approximation. Many new satellites with different symmetries from the mainline were discovered. The photodissociation fragments of core-excited and ionized N_2 were measured in coincidence with low energy electrons as functions of the vibrationally resolved incident light energy. The kinetic energy distributions of the fragments were determined and compared with the calculated energies for the dissociative potentials. Excess vibrational energy at the 1s to pi* transition does not appear as kinetic energy of the dissociative fragments. Highly energetic dissociative states are present, which must result from triply charged N_2.. The photodissociation fragments of C_2 H_4 and CH_3 Cl were measured in coincidence were low energy electrons near the C 1s ionization threshold. For C _2H_4, the 4s Rydberg state can relax via participant Auger decay to stable C _2H_4^+. Quasi stable C_2H_4 ^{+2} is also present. Energetic fragments are correlated with the electron impact Auger spectrum. For CH_3Cl, the dissociation pattern is very similar for the entire C 1s ionization region. Subtile differences are present. Cl^ {+2} is less intense at the C 1s to 4pe transition.