ABSTRACT
The multiphoton ionization of H2 has been studied using laser pulses of 266 nm wavelength, 250 fs duration, and 5x10(13) W/cm(2) peak intensity. Dissociation of H2(+) via one-photon absorption proceeds through two channels with markedly different proton angular distributions. The lower-energy channel (2.6 eV kinetic energy release) is produced in the bond softening mechanism, which generates parallel alignment. The higher-energy channel (3.5 eV) originates from population trapping in a light-induced bound state, where bond hardening generates orthogonal, counterintuitive alignment.
ABSTRACT
The field of atomic and molecular photoionization has undoubtedly been transformed by the use of synchrotron radiation. In the mid-1960's the 180 MeV electron synchrotron at the National Bureau of Standards, Washington, DC, was used to discover many resonances in the photoionization continua of atoms and simple molecules. The resonances were characterized in terms of the excited states involved, their energies and lifetimes. This article concentrates on that period. As dedicated high-flux storage rings became available, the emphasis turned to the study of the products of the photoionization process in order to further understand the electron correlation effects that had been uncovered earlier; examples of these more sophisticated experiments are given.
ABSTRACT
In some cases there are hidden correlations in a highly fluctuating signal, but these are lost in a conventional averaging procedure. Covariance mapping allows these correlations to be revealed unambiguously. As an example of the applicability of this technique, the dynamics of fragmentation of molecules ionized by an intense picosecond laser are analyzed.
ABSTRACT
A total of 153 krypton resonances in the spectral region 330-500 Å and 253 xenon resonances in the spectral region 375-600 Å are reported. A detailed listing of the resonances is given, with wavelength and line shape information. The analysis of the spectra is very incomplete and will require detailed theoretical calculation to significantly improve it. In Kr, 45 resonances and in Xe, 56 resonances have been grouped into probable Rydberg series, for which classifications are suggested. The resonances are due, in the main, to either the excitation of the inner subshell "s" electron (s 2 p 6 â sp 6 np) or to the excitation of two of the outer "p" electrons simultaneously (s 2 p 6 â s 2 p 4 nln'l'). These high-lying excited states autoionize, resulting in resonances with window-, asymmetric-, or absorption-type profiles. Where possible, comparisons are made with previous work.
ABSTRACT
Electron synchrotrons are becoming increasingly important as sources of extreme uv radiation for physical experiments. The NBS 180-MeV machine has been utilized for gas absorption studies over a four-year period, during which a 3-m grazing incidence spectrograph and monochromator have been designed, constructed and put into operation. The instruments are extremely stable to vibration and temperature variation, and are operating with a slit limited resolution of the order of 0.06 A. The design principles and features of these instruments are described, and a highly successful prealignment procedure for grazing incidence spectrometers is outlined. The effect of the unusual characteristics of this light source on the illumination and performance of the spectroscopic instruments is discussed.
ABSTRACT
A comparison has been made between a calibrated thermopile and an argon ionization chamber as absolute detectors of radiant flux of wavelengths 584 A and 735 A. Corrections were applied to the data in order to account for the absorption due to gases in the monochromator, the energy carried away from the thermopile by photoejected electrons, nonuniformity of response across the surface of the thermopile, and uneven illumination of the thermopile by the flux from the monochromator. The two detectors were found to agree within the 3% estimated probable error in the measurements.
