Resonant multiphoton ionization spectra of molecules and molecular fragments. Technical report, October 1987--September 1988

The objective of our research under this contract is to carry out studies of resonant enhanced multiphoton ionization (REMPI) processes in molecules. In the (n + 1) - REMPI process of interest an atom or molecule in a specific initial state absorbs n photons making a transition to an intermediate state from which it is subsequently ionized by absorption of an additional photon. A remarkable feature of resonant enhanced multiphoton ionization is that the narrow bandwidth radiation of lasers makes it possible (i) to select a specific rovibrational level in the initial state of a molecule or fragment, (ii) to resonantly pump this level up to a selected rotational-vibrational level of an excited electronic state, and (iii) to subsequently photoionize the state that has been resonantly excited. The extreme state-selectivity and sensitivity make REMPI both a tool with several practical applications and an important technique for probing the photoionization dynamics of vibrationally and electronically excited states. Some significant applications of this technique include its use for state-specific detection of species and diagnostics in combustion and chemical etching media and plasmas, (ii) for state-specific generation of molecular ions for use in ion-molecule reaction studies, and (iii) as a probe of photofragmentation and gas-surface scattering including alignment and orientation effects in these processes