Time-of-flight mass spectrometry (concepts, achievements, and prospects)

Using the technique of laser ionization mass spectrometry, studies have been carried out of multiphoton ionization (MPI) and fragmentation of molecules under collision‐free conditions. MPI spectra and mass fragmentation patterns are obtained via irradiation of isolated molecules by a pulsed, tunable dye laser focused down on a molecular beam traversing the ion‐source region of a quadrupole mass filter. At each resonance, corresponding to m‐photon ionization of an n‐photon‐excited intermediate state, the fragmentation pattern of the ions is measured. Resonance‐enhanced MPI/mass spectra provide detailed information on the identity and relative abundances of the ionic fragments formed in the overall n+m photoionization process. From a knowledge of the appearance potentials of the various fragment ions, the minimum number of photons absorbed per molecule can be deduced. Increasing the laser pulse peak energy (or fluence) increases the average number of photons absorbed and thus the extent of fragmentation. Ho...

Resonance‐enhanced multiphoton ionization and fragmentation of molecular beams: NO, I2, benzene, and butadiene

A review of the applications to solids of the laser ion source in mass spectrometry

It is now known that tunable dye laser light leads to resonance enhanced photoionization of molecules in a mass spectrometer via multiphoton absorption. In some cases this process also leads to ion fragmentation. Time delayed tandem laser pulses of different wavelengths are employed to study the mechanism of this multiphoton ionization and fragmentation process in benzene. The experimental results strongly indicate that excitation does not proceed up an autoionization ladder of the neutral molecule, rather the multiphoton process is shown to be due to the climbing of two independent ladders, one up to the ionization potential in the neutral molecule, the second in the new species of molecular parent ions produced. Hence multiphoton ionization could also form a new basis of ion spectroscopy.

Visible and UV multiphoton ionization and fragmentation of polyatomic molecules

Molecular beams of azulene and naphthalene are irradiated by the output of a tunable pulsed laser and the charged species produced by multiphoton ionization (MPI) are analyzed using a quadrupole mass spectrometer. A study of the ion fragmentation pattern as a function of laser power and laser wavelength permits these two C10H8 isomers to be readily distinguished. Compared to electron impact (EI) ionization, the MPI process can produce more gentle ionization at low laser powers and more extensive fragmentation at high laser powers. The former permits the study of azulene and naphthalene dimers from which their heats of dissociation are estimated. In the case of azulene, two‐color excitation yields a mass spectrum that differs from the mass spectrum obtained by excitation with either color, alone. The ionization efficiency of MPI is very high, exceeding that of EI during the time the pulsed laser is on. A qualitative description involving autoionizing states is presented to account for this efficiency and t...

Multiphoton ionization of azulene and naphthalene

Laser spectroscopy and kinetic mass spectrometry of polyatomic isolated molecules have been carried out by using stepwise laser ionization of molecules in a mass spectrometer The optical absorption spectrum of NO(2) has been recorded, for example, by using pulsed dye-laser excitation and H(2) vacuum-ultraviolet laser ionization of molecules The kinetics of excited electron states and of the production of molecular and fragmented ions of some polyatomic molecules have been investigated with high temporal resolution The sensitivity achieved is 10(-10) cm(-1) of the absorption coefficient and 10(9) (10(5)) molecules in the ground (electronically excited) state in the irradiated volume

Stepwise laser photoionization of molecules in a mass spectrometer: a new method for probing and detection of polyatomic molecules.

Two-step photoionization of H2CO by radiation of N2− and H2− lasers and measurement of the lifetime of its 1A2 state

Photoionization of molecules by VUV laser radiation

Hydrogen Laser in Vacuum Ultraviolet at Atmospheric Pressure

Superradiance was emitted from an ultraviolet nitrogen laser using a transversely excited open air cell. The laser was excited with a parallel-plate Blumlein discharge line. The output power was several tens of kilowatts when the line charging voltage was ~30 kV. The continuous charging of the Blumlein line had the advantages of technological simplicity and relatively long service life.

V. S. Antonov

Papers

Stepwise laser photoionization of molecules in a mass spectrometer: a new method for probing and detection of polyatomic molecules.

Two-step photoionization of H2CO by radiation of N2− and H2− lasers and measurement of the lifetime of its 1A2 state

Photoionization of molecules by VUV laser radiation

Hydrogen Laser in Vacuum Ultraviolet at Atmospheric Pressure

Output radiation of an ultraviolet nitrogen laser excited transversely in an open air cell