This paper ends the series of reviews on multiple photon IR laser photophysics and photochemistry. The applications of IR MP processes in fundamental chemical studies and chemical technology are considered.

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In response to the growing experimental evidence of the importance of nonlinear phenomena in ion trap operation, a new theoretical model of ion ejection is developed. The pseudopotential well approximation for forced ion oscillations in an ion trap under the conditions of ion-molecule collisions is modified to include octapole perturbations on the quadrupole field. Ion ejection is investigated using the first-order Mitropol'skii asymptotic method for both infinitesimal and finite scan rates. It is shown that the combined action of collisional damping and nonlinearity distorts the resonance curve in such a way that "quenching" of oscillations takes place. As a result, with appropriate excitation and direction of scanning, the amplitude increases as if no damping exists! The main characteristics of the jump are derived as functions of scan rate and used for analytical estimation of mass resolution, mass peak width, and excitation voltage. Satisfactory agreement between calculated and experimental peak widths is demonstrated for the range of scanning rates in excess of 6 orders of magnitude.

Simulations of the spectra of vibrational transitions in highly vibrationally excited XY6 molecules at certain energy E vib are performed. The infrared (IR) transitions in the mode ν3 of the molecules SF6 and WF6 as well as the Raman ones in the mode ν1 of SF6 are studied. The shapes and parameters of the spectral bands, such as the integral intensity, the mean frequency, and the width, are obtained in a wide range of E vib. The calculated widths prove to be much broader than the expected contributions to them because of intramolecular vibrational relaxation (IVR); this indicates the dominant role of statistical inhomogeneous broadening in the width formation for the investigated molecules.

This paper begins our review paper on the multiple-photon excitation of molecules by intense infrared laser light. The whole review will be given in installments. In this first part we bring forward certain general concepts on spectroscopy, molecular physics and chemical kinetics essential for understanding the later material.