Volume 128, Issue 2, 14 January 2008
Index of content:
128(2008); http://dx.doi.org/10.1063/1.2829111View Description Hide Description
We show that weak residual magnetic fields can significantly affect the preparation and measurement of molecular rotational angular momentum alignment in a typical gas-phase stereodynamics apparatus. Specifically, polarizationspectroscopy, a third-order nonlinear spectroscopic technique, is used to prepare and probe the collisional and noncollisional losses of rotational angular momentum alignment of OH . Residual magnetic fields of the order of the geomagnetic field are shown to have a significant effect on the prepared polarization on a submicrosecond timescale. This can be expected to be a significant effect for many gas-phase free radicals, such as those of interest in combustion, atmospheric chemistry, and the burgeoning field of cold molecules. We demonstrate a simple experimental remedy for this problem.
128(2008); http://dx.doi.org/10.1063/1.2828553View Description Hide Description
cations are probed with infrared photodissociationspectroscopy in the region using the method of rare gas tagging. The ions and their complexes with Ar or are produced in a pulsed electric discharge supersonic expansion cluster source. Two structural isomers are characterized, namely, the allyl and 2-propenyl cations. The infrared spectrum of the allyl cation confirms previous theoretical and condensed phase studies of the charge delocalized, resonance-stabilized structure. The 2-propenyl cation spectrum is consistent with a symmetry structure having a nearly linear CCC backbone and a hyperconjugatively stabilizing methyl group.
Theoretical characterization of temperature and density dependence of liquid water electronic excitation energy: Comparison with recent experimental data128(2008); http://dx.doi.org/10.1063/1.2826325View Description Hide Description
In a recent paper [Aschi et al., ChemPhysChem6, 53 (2005)], we characterized, by means of theoretical-computational procedures, the electronic excitation of water along the typical liquid state isochore for a large range of temperature. In that paper we were able to accurately reproduce the experimental absorption maximum at room temperature and to provide a detailed description of the temperature dependence of the excitation spectrum along the isochore. In a recent experimental work by Marin et al. [J. Chem. Phys.125, 104314 (2006)], water electronic excitation energy was carefully analyzed in a broad range of density and temperature, finding a remarkable agreement of the temperature behavior of the experimental data with our theoretical results. Here, by means of the same theoretical-computational procedures (molecular dynamics simulations and the perturbed matrix method), we investigate water electronic absorption exactly in the same density-temperature range used in the experimental work, hence, now considering also the absorption density dependence. Our results point out that, (1) for all the densities and temperatures investigated, our calculated absorption spectra are in very good agreement with the experimental ones and (2) the gradual maxima redshift observed increasing the temperature or decreasing the density has to be ascribed to a real shift of the lowest electronic transition, supporting the conclusions of Marin et al.