Multiphoton ionization of ammonia: Mass analysis and photoelectron spectra

Journal Article · Thu Jul 01 04:00:00 EDT 1982 · J. Chem. Phys.; (United States)

DOI:https://doi.org/10.1063/1.443602· OSTI ID:5319486

Glownia, J H; Riley, S J; Colson, S D; Miller, J C; Compton, R N

Mass and photoelectron spectra following the resonantly enhanced four-photon ionization of ammonia have been recorded. The mass spectral data show that extensive fragmentation occurs at a distinct wavelength threshold. This threshold energetically corresponds to the minimum number of photons required to reach the first excited state of the ion. The branching ratio for the various fragments (H/sup +/, H/sup +//sub 2/, N/sup +/, NH/sup +/, NH/sup +//sub 2/, NH/sup +//sub 3/) is independent of the neutral resonantly excited vibronic state, and the ratios differ from those recorded by conventional ionization techniques. Photoelectron energy measurements show that low (approx.0 eV) kinetic energy electrons are produced following ionization of all but one of the resonantly excited Rydberg states investigated. The origin of these zero energy electrons is thought to be due to vibrational autoionization. Internal conversion may give rise to the neutral vibronic levels responsible for the autoionization. For one excited state, higher electron energies are recorded corresponding to direct ionization. This mechanism leaves the positive ion in a single vibrational quantum state which is the same vibrational state as that of the initially excited neutral-ammonia with cross sections governed by the Franck--Condon principle. The results suggest that the fragmentation occurs entirely within the ionic manifold.

• Research Organization: University of California, Los Alamos National Laboratory, Los Alamos, New Mexico 87545
• OSTI ID: 5319486
• Journal Information: J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 77:1; ISSN JCPSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400104* -- Spectral Procedures-- (-1987)
AMMONIA
AUTOIONIZATION
CONVERSION
DECAY
ELECTROMAGNETIC RADIATION
ELECTRON SPECTROSCOPY
ENERGY
ENERGY LEVELS
EXCITED STATES
HYDRIDES
HYDROGEN COMPOUNDS
INTERNAL CONVERSION
IONIZATION
LASER RADIATION
MASS SPECTRA
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
PHOTOELECTRON SPECTROSCOPY
PHOTOIONIZATION
RADIATIONS
RESONANCE
SPECTRA
SPECTROSCOPY
THRESHOLD ENERGY
VIBRATIONAL STATES