Volume 121, Issue 16, 22 October 2004
Index of content:
121(2004); http://dx.doi.org/10.1063/1.1810138View Description Hide Description
For clusters of N-methylacetamide and water molecules the performance of the fixed-charged approximation was tested against continuum and explicit ab initio models. The dispersion of the vibrational frequencies when constant electrostatic potential was maintained at the solute atoms was compared to the distribution caused by geometry fluctuations.
121(2004); http://dx.doi.org/10.1063/1.1808416View Description Hide Description
The NH–He van der Waals complex was characterized via laser excitation of bands associated with the NH transition. It was demonstrated that the ground state supports a bound level with a rotational constant of B ″=0.334(2) cm−1. These results are in agreement with the predictions of recent high-level theoretical calculations. Spin–orbit predissociation of the excited complex was observed, and the spectra yield insights regarding the NH(A)+He potential energy surfaces.
121(2004); http://dx.doi.org/10.1063/1.1809118View Description Hide Description
Two types of anion states are shown to coexist in nanometer-scale polyacene cluster anions. Naphthalene and anthracenenanoclusters having a single excess electron were produced in the gas-phase. Photoelectron spectra of size-selected cluster anions containing 2 to 100 molecules revealed that rigid “crystal-like” cluster anions emerge, greater than ∼2 nanometers in size, and coexist with the “disordered” cluster anion in which the surrounding neutral molecules are reorganizing around the charge core. These two anion states appear to be correlated to negative polaronic states formed in the corresponding crystals.
Optimal linearized Poisson–Boltzmann theory applied to the simulation of flexible polyelectrolytes in solution121(2004); http://dx.doi.org/10.1063/1.1808411View Description Hide Description
Optimal linearized Poisson–Boltzmann (OLPB) theory is applied to the simulation of flexible polyelectrolytes in solution. As previously demonstrated in the contexts of the cell model [H. H. von Grünberg, R. van Roij, and G. Klein, Europhys. Lett. 55, 580 (2001)] and a particle-based model [B. Beresfordsmith, D. Y. C. Chan, and D. J. Mitchell, J. ColloidInterface Sci. 105, 216 (1985)] of chargedcolloids, OLPB theory is applicable to thermodynamic states at which conventional, Debye–Hückel (DH) linearization of the Poisson–Boltzmann equation is rendered invalid by violation of the condition that the electrostatic coupling energy of a mobile ion be much smaller than its thermal energy throughout space, As a demonstration of its applicability to flexible polyelectrolytes, OLPB theory is applied to a concentrated solution of freely jointed chains. The osmotic pressure is computed at various reservoir ionic strengths and compared with results from the conventional DH model for polyelectrolytes. Through comparison with the cylindrical cell model for polyelectrolytes, it is demonstrated that the OLPB model yields the correct osmotic pressure behavior with respect to nonlinear theory where conventional DH theory fails, namely at large ratios of mean counterion density to reservoir salt density, when the Donnan potential is large.
121(2004); http://dx.doi.org/10.1063/1.1804496View Description Hide Description
In this work we demonstrate that a doubly hydrogen-bonded interface of two carboxylic acid groups behaves as efficient conduit to transmit the rotor effects for IVR acceleration in a phenyl ring. The phenomenon has been demonstrated by measuring the resolved emission spectra following SVL excitations in of a 1:1 mixed dimer between acetic acid and benzoic acid. The role of the methyl rotor has been ascertained by comparing the results with those obtained for an analogous dimeric system between formic acid and benzoic acid.