Spectroscopy photoionization

The above fomuilae for the absorption spectrum can be applied, with minor modifications, to other one-photon spectroscopies, for example, emission spectroscopy, photoionization spectroscopy and photodetachment spectroscopy (photoionization of a negative ion). For stimulated emission spectroscopy, the factor of fflj is simply replaced by cOg, the stimulated light frequency however, for spontaneous emission... 

The temi action spectroscopy refers to those teclmiques that do not directly measure die absorption, but rather the consequence of photoabsorption. That is, there is some measurable change associated with the absorption process. There are several well known examples, such as photoionization spectroscopy [47], multi-photon ionization spectroscopy [48], photoacoustic spectroscopy [49], photoelectron spectroscopy [, 51], vibrational predissociation spectroscopy [ ] and optothemial spectroscopy [53, M]. These teclmiques have all been applied to vibrational spectroscopy, but only the last one will be discussed here. 

C. L. Wilson, Comprehensive Analytical Chemisty Ultraviolet Photoelectron and Photoion Spectroscopy Auger Electron Spectroscopy Plasma Excitation in SpectrochemicalAnalysis, Vol. 9, Elsevier Science, Inc., New York, 1979. 

Molecular Fluorescence Spectroscopy Photometric Titrations Analytical Applications of Interferometry Vol. 9 Ultraviolet Photoelectron and Photoion Spectroscopy... 

Photoionization Spectroscopy of Dichromium and Dimolybdenum Ionization Potentials and Bond Energies. 

Letokhov, V. S., Laser Photoionization Spectroscopy, Academic Press, San Diego, 1987. 

Figure 1. Versions of photoionization spectroscopy wherein not only the dependence of the multiphoton ionization efficiency on the laser wavelength is subject to measurement, but also the mass spectrum of photons and energy spectrum of photoelectrons (a) energy-level diagram (b) collision of a neutral particle with laser photons.

This is a severe drawback in the case of equilibrium studies of metal molecules since, as a rule, such molecules are minor vapor components and maximum sensitivity is required for their thermodynamic evaluation. However, very precise ionization potentials can be measured using photoionization spectroscopy (5,28). Berkowltz (28) reviewed early work concerning alkali metal dimers. Herrmann et al. ( ) have measured the ionization potentials of numerous sodium, potassium and mixed sodium-potassium clusters. For most of these clusters the atomization energies of the neutral molecules are not known. Therefore, the dissociation energies of the corresponding positive ions cannot be calculated. 

Two-colour photoionization spectroscopy of aniline cooled in a supersonic jet. Strong propensity for vertical (An = 0) ionization allows vibrational frequencies of CgHgNH2 ( B,) to be determined Two-colour photoacoustic and MPI spectra of aniline, determined as a function of time delay between the two laser pulses. Observed both ionization and dissociation t MPI/TOF mass spectrometric study of phenol. Mechanism of ionization and ion fragmentation t MPI/TOF mass spectrometric study of fragmentation patterns in benzaldehyde. Strong wavelength dependence observed at 266 and 355 nm. Results show operation of two different mechanisms at these excitation wavelengths... 

Oscillator strengths or absorption cross sections may be obtained by applying saturation spectroscopy techniques to multistep photoionization spectroscopy. A few transitions in uranium have been studied.One of the advantages of saturation spectroscopy is that it can be applied to any one of the steps in the schemes shown in Fig. 2. The disadvantages are that the experimental requirements are severe (laser-atomic beam interaction area,-frequency,-band width and-polarization) and interpertation of the data can be complex. A detailed discussion will not be given because little application has been made to the lanthanides and actinides. We will discuss in the Autoionization section the determination of photoionization cross sections by a saturation method. 

Uncovering two-step autoionisation involved a combination of techniques the photoabsorption spectrum of Ba was obtained using synchrotron radiation and classical spectroscopy of high dispersion [358]. The analysis was performed using the multiconfigurational Dirac-Fock method, which allowed the limits to be identified [359]. The doubleionisation spectrum was obtained by photoion spectroscopy using syn-... 

Although most suitable for use with lasers, Thermionic diodes have also been successfully applied to synchrotron radiation studies by using wiggler magnets to enhance the intensity of the beam [390]. Last but not least, one should mention the important category of atomic beam experiments, complemented by the techniques of photoelectron and photoion spectroscopy. All these techniques are suitable for the experimental study of interacting resonances. We turn now to their theoretical description, which will be illustrated by experimental examples. 

V.S. Letokhov, Laser Photoionization Spectroscopy (Academic, New York 1987)... 

Browning R (1979) Ultraviolet photoelectron and photoion spectroscopy. In Svehla G, ed. Wilson and Wilsoris Comprehensive analytical chemistry, Vol 9, pp. 1—88. Elsevier, Amsterdam. 

Kni Knight, A.A., Stangassinger, A., Duncan, M.A. Photoionization spectroscopy of Au-Ar, Chem. Phys. Lett. 273(1997) 265-271. 

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