THEORETICAL SPIN-ORBIT SPECTROSCOPY OF Cl DOPANTS IN SOLID PARAHYDROGEN
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Date
2012
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Ohio State University
Abstract
Solid parahydrogen (pH$_2$) matrices containing open-shell ($^2$P) Cl and Br atoms as substitutional impurities exhibit several infrared (IR) absorption features associated with intermolecular interactions between the halogen atom and nearby pH$_2$ molecules., 021106 (2007); S.~C.~Kettwich, L.~O.~Paulson, P.~L.~Raston and D.~T.~Anderson, J.\ Phys.\ Chem.\ A {\bf 112}, 11153 (2008).} These dopant-induced IR absorption features are associated with (i) spin-orbit (SO) excitation of the halogen atom, and (ii) cooperative excitations in which a single IR photon both triggers SO excitation of the halogen atom and excites the H-H stretching coordinate of a nearby pH$_2$ molecule. The IR spectral features thus contain detailed information about the interaction between the open-shell halogen atom and the surrounding pH$_2$ molecules, and in particular tell us about the coupling between the atom's electronic degrees of freedom and the nuclear motion of its H$_2$ neighbors. Here we present recent progress towards understanding these features in Cl-doped solid pH$_2$. This system represents an arena for testing theoretical approaches that generate many-body, non-pairwise-additive potential energy functions for the dopant--matrix interaction by combining multiple low-lying Cl--H$_2$ pair potential energy functions. Our analysis must account for the fact that the individual pH$_2$ molecules in the doped solid undergo large amplitude zero-point motions;, 393 (1980).} we use quantum Monte Carlo simulations, 2339 (2011).} to model these zero-point motions. We interpret our findings in terms of a reduced dimensionality model that provides a qualitative understanding of the role that matrix zero-point motions play in the observed spectra.
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Author Institution: Department of Chemistry, University of Tennessee, Knoxville, TN 37996 USA