[en] This book is Volume 35 in Springer's Topics in Current Physics series designed to provide the interested reader perspective on a rapidly developing research field by gathering together review articles by major players. The editor has accurately highlighted the major results of the multiple-photon excitation (MPE) shock wave of research activity that propagated through the gas-phase chemical physics community during the 1970's. Throughout this period three questions intrigued the photochemists: (1) how is it possible that virtually any polyatomic molecule can efficiently absorb scores of infrared photons from a pulsed CO₂ TEA laser to achieve bond fission? (2) can insight into the dissociation dynamic be gained from this process, and in particular can bonds be made to break selectively? (3) could MPE be used to separate heavy isotopes? The answers to the first two questions are thoroughly examined and answered in the excellent review by Y.T. Lee et al., which itself is worth the price of the book. The question of isotope separation is discussed in two articles, one by Ambartzumian and the other by Cantrell. However, the recent glut of cheap uranium on world energy markets and the decision of DOE to develop atomic multiphoton ionization as the process of choice have resulted in a rapid deflation of interest in MPE separation schemes

[en] A method and apparatus for laser isotope separation of atoms or molecules. The method for laser isotope separation comprises the irradiation of an atom or molecule to produce an adiabatic population inversion, terminating the radiation sufficiently abruptly to trap the atom or molecule in an excited state, and further radiating the atom or molecule for causing transitions out of the previously excited state for dissociating the molecule or for causing a chemical reaction to effect isotopic separation. The method comprises slowly increasing the intensity of the initial radiation from zero to a value sufficiently high to produce an adiabatic population inversion when the frequency is tuned near a single narrow resonance which includes the overlapping multiphoton resonances originating from either the rotational energy levels of the vibrational ground state of the molecule or the different hyperfine levels of the ground state of the atom for providing the adiabatic population inversion. The apparatus for laser isotope separation comprising a first irradiation means that provides a slowly increasing continuum of intensity from zero to a sufficiently high value to produce an adiabatic population inversion when the frequency is tuned near a single narrow resonance associated with the atom or molecule, a second irradiation that produces radiation having an appropriate wave length, an intensity sufficient to cause transitions out of the previously excited state and a smooth, shorter pulse shape than required for the first irradiation means, and a Raman shifting cell, utilized with the first and second irradiation means for shifting the wave length of the radiation as needed

[en] An infrared laser system and method for isotope separation may comprise a molecular gas laser oscillator to produce a laser beam at a first wavelength, Raman spin flip means for shifting the laser to a second wavelength, a molecular gas laser amplifier to amplify said second wavelength laser beam to high power, and optical means for directing the second wavelength, high power laser beam against a desired isotope for selective excitation thereof in a mixture with other isotopes. The optical means may include a medium which shifts the second wavelength high power laser beam to a third wavelength, high power laser beam at a wavelength coincidental with a corresponding vibrational state of said isotope and which is different from vibrational states of other isotopes in the gas mixture

[en] The master equation for cluster growth and evaporation is derived from many-body quantum mechanics and from a modified version of quantum damping theory used in laser physics. For application to nucleation theory, the quantum damping theory has been generalized to include system and reservoir states that are not separate entities. Formulae for rate constants are obtained. Solutions of the master equation yield equations of state and system-averaged quantities recognized as thermodynamic variables. Formulae for Helmholtz free energies of clusters in a Debye approximation are derived. Coexistence-line equations for pressure volume, and number of clusters are obtained from equations-of-state analysis. Coexistence-line and surface-tension data are used to obtain values of parameters for the Debye approximation. These data are employed in calculating both the nucleation current in diffusion cloud chamber experiments and the onset of condensation in expansion nozzle experiments. Theoretical and experimental results are similar for both cloud-chamber and nozzle experiments, which measure water

[en] Recent theoretical studies of coherent propagation effects in SF₆ and other polyatomic molecules are summarized beginning with an account of relevant aspects of the high-resolution spectroscopy of the ν₃ band of SF₆. A laser pulse propagating in a molecular gas can acquire new frequencies which were not initially present in the pulse, and, in fact, a wave is coherently generated at the frequency of every molecular transition accessible from the initial molecular energy levels. The possible consequences of coherent generation of sidebands for the multiple-photon excitation of SF₆ and other polyatomic molecules are discussed

No abstract available

[en] In this chapter we review the theoretical tools and concepts needed for a first-principles quantum-mechanical study of the coherent laser excitation of polyatomic molecules under collision-free conditions, and illustrate these methods with selected numerical results. (orig./WL)

[en] An infrared laser system and method for isotope separation may comprise a molecular gas laser oscillator to produce a laser beam at a first wavelength, raman spin flip means for shifting the laser to a second wavelength, a molecular gas laser amplifier to amplify said second wavelength laser beam to high power, and optical means for directing the second wavelength, high power laser beam against a desired isotope for selective excitation thereof in a mixture with other isotopes. The optical means may include a medium which shifts the second wavelength high power laser beam to a third wavelength, high power laser beam at a wavelength coincidental with a corresponding vibrational state of said isotope and which is different from vibrational states of other isotopes in the gas mixture

[en] The history, basic requirements, parameters, process efficiency, and economics of the laser isotope separation process are discussed. Isotope effects, single-photon processes, several-photon processes, and multiple photon photodissociation are considered

[en] The full isotopic character of multiquantum amplitudes is discussed. Of particular importance are the roles of enhanced isotopic effects generally characteristic of molecular perturbed spectra and the complete utilization of all the available optical field variables. Examples involving NH₃, CH₃Br, and SF₆ are examined. Multiquantum excitation of molecules leading to dissociation and excitation of highly excited vibrational states is now a commonly observed phenomenon. These processes have been observed under both collision-free conditions, as well as those involving considerable collisional interaction. It is also clear that multi-quantum amplitudes can be applied generally to nearly all classes of molecular systems. This generality has been explicitly demonstrated in experiments on ammonia, formaldehyde, sulfur hexafluoride, boron trichloride, and osmium tetraoxide, to mention a few of the molecules with which direct experimental results have been obtained. Strong isotopic signatures in these excitation mechanisms have also been observed, with results reported on sulfur hexafluoride, osmium tetraoxide, formaldehyde, boron trichloride, and molybdenum hexafluoride. In this analysis we will examine the ways in which multiquantum amplitudes exhibit their isotopic character. We will emphasize the manner in which the various optical degrees of freedom under our control can be utilized to optimize the isotopic differentialsexpressed by the molecular system. These considerations involve a mapping of the optical degrees of freedom onto the relevant motions of the molecular species. As a prelude to this discussion, however, we will begin with a review of some simple properties of electromagnetic fields and molecular systems