We have measured two-dimensional photoelectron momentum spectra of Ne, Ar, and Xe generated by 800-nm, 100-fs laser pulses and succeeded in identifying the spectral ridge region (back-rescattered ridges) which marks the location of the returning electrons that have been backscattered at their maximum kinetic energies. We demonstrate that the structural information, in particular the differential elastic scattering cross sections of the target ion by free electrons, can be accurately extracted from the intensity distributions of photoelectrons on the ridges, thus effecting a first step toward laser-induced self-imaging of the target, with unprecedented spatial and temporal resolutions.

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When an electron from a diatomic molecule undergoes tunneling-rescattering ionization, a novel form of destructive interference can be realized that involves all four geometric orbits that are available to the electron when it is freed, because both ionization and rescattering may take place at the same or at different centers. We find experimentally and confirm theoretically that in orientation-averaged angle-resolved high-order above-threshold ionization spectra the corresponding destructive interference is visible for O_{2} but not for N_{2}. This effect is different from the suppression of ionization that is well known to occur for O_{2}.

Allyl radicals were generated by the photolysis of 1,5-hexadiene at 193 nm and were detected by observing the Vll, i.e., CH 2 symmetric wagging band by infrared diode laser kinetic spectroscopy. The observed spectrum showed clearly the effect of nUclear-spin statistical weights, establishing the presence of a q axis in the molecule. The spin-rotation splitting was not resolved; only some high-Ka lines were found broader than others, placing an upper limit for the Eaa constant at about 200 MHz or less. The rotational constants derived from the observed spectrum indicate that the molecule is essentially planar. The C-C bond length and the CCC bond angle were calculated from the ground-state rotational constants to be 1.3869 A and 123.96°, respectively, where structural parameters involving hydrogens were fixed to those of ab initio values.