Index of content:
Volume 119, Issue 17, 01 November 2003
Circular dichroism in the photoelectron angular distribution from randomly oriented enantiomers of camphor119(2003); http://dx.doi.org/10.1063/1.1621379View Description Hide Description
Circular dichroism in the angular distribution of valence photoelectrons emitted from randomly oriented chiral molecules has been observed in experiments that use circularly polarized VUVsynchrotron radiation.Photoionization of the outermost carbonyl oxygen lone pair electrons from pure enantiomers of the prototype chiral molecule camphor is shown to have an asymmetry in the forward–backward scattering of photoelectrons (relative to the propagation direction of the light beam) of magnitude approaching 3% at 9.2 eV photon energy. The asymmetry reverses on exchange of either the helicity of the radiation or of the molecular enantiomer, confirming theoretical predictions of an effect that arises in the pure electric-dipole approximation.
119(2003); http://dx.doi.org/10.1063/1.1620997View Description Hide Description
The reaction is studied to understand the effect of vibrational excitation on the reaction pathways. The hydrogen molecules in the levels are populated by using stimulated Raman pumping (SRP). A pump–probe technique is employed simultaneously to initiate the reaction and monitor the products. The pump–SRP and SRP–probe delay time are short enough to allow for the products to be in a nascent state. The population fraction in the level can be estimated to be 7.5% by using coherent anti-Stokes Raman spectroscopy. As characterized by Boltzmann rotational temperature of 730 K, the rotational state distributions of obtained with appear to be unimodal, similar to those obtained with but the product yield is enhanced by a factor of 7–8 times. According to the potential energy surfaces calculations, the insertion mechanism in (near) collision configuration is favored. The collision is initially along the surface in the entrance channel and then transits to the ground surface, from which the products are formed. When stretches to its outer turning point (∼0.9 Å), the surface may diabatically couple to the surface in the attractive region. An energy barrier of 4300 cm−1 will otherwise obscure the reaction if the bond distance is fixed at 0.75 Å. The energy deposited in the level simply enlarges the bond distance to help facilitate the reaction and increase the subsequent product yield. The lack of detection of the product implies that the exoergic energy by 2530 cm−1 should not be distributed statistically among different freedom of motions. The vibrational excitation does not seem to open up an additional pathway for the reaction.
119(2003); http://dx.doi.org/10.1063/1.1622379View Description Hide Description
We report a potential energy surface and calculations of power spectra for The potential surface is obtained by precise fitting of MP2/cc-pVTZ electronic energies and gradients, which are obtained in classical direct-dynamics calculations. The power spectra are obtained using standard microcanonical classical and novel quasiclassical calculations of the velocity autocorrelation function, from which the power spectrum is obtained in the usual way. Both calculations agree qualitatively that the overall spectrum is quite complex; however, the latter calculations indicate that some spectral features may be assignable.