Theoretical study of resonance formation in microhydrated molecules. I. Pyridine-(H2O)n, n = 1,2,3,5

Abstract

We present R-matrix calculations for electron scattering from microhydrated pyridine. We studied the pyridine-HO cluster at static-exchange (SE), SE + polarization, and close-coupling levels, and pyridine-(HO) n = 2, 3, and 5 at SE level only in order to investigate the effect of hydrogen bonding on the resonances of pyridine. We analyse the results in terms of direct and indirect effects. We observe that the total (direct plus indirect) effect of microhydration leads to the stabilization of all resonances studied, both shape and core-excited. The size of the shift is different for different resonances and seems to be linked to the dipole moment of the cluster.

Electron collisions with molecules and molecular clusters

“…Although both our [34] and the earlier SMC calculations performed both at SE and SEP level showed that similar conclusions were reached for both types of calculations, inclusion of the polarization effects in a consistent way should provide a more accurate picture and improve our understanding of microhydration effects.…”

“…Using the R-matrix method and the UKRmol+ suite, extensive studies of pyridine-(H 2 O) n and thymine-(H 2 O) n with n=1, 2, 3, 5 were performed [34,35] at the SE level in order to understand the effect of microhydration on the two lowest π * shape resonances present in both ring molecules (see, for example, [36,37]). Earlier studies [38] using the Schwinger multichannel method (SMC) for the π * shape resonance of formic acid in clusters with 1 and 2 water molecules showed that: (i) the effect of water on the resonance position depended on whether H 2 O was the hydrogen donor/acceptor in the hydrogen bond, with the former leading to a lowering of the resonance energy and the latter to an increase; (ii) the effect was qualitatively additive.…”

“…Table 2. Energy shifts, in eV, for the first and second (π * ) resonance in pyridine upon hydrogen bonding with a single water molecule calculated at SE level using the cc-pVDZ basis set (further details in [34]). The direct and indirect contributions and the total effect are listed.…”

“…See text for details. The orbital was determined with MOLPRO [40] in a SCF Hartree-Fock calculation using the cc-pVDZ basis set and a geometry optimized as described in [34].…”

UKRmol+: A suite for modelling electronic processes in molecules interacting with electrons, positrons and photons using the R-matrix method

“…The suite is able to model electronic excitation for small and mid-size molecules very accurately as well as describe their coreexcited resonances [71,72]. Among the largest targets studied (in terms of number of atoms in the system) are the molecular clusters pyridine-(H 2 O) 5 and thymine-(H 2 O) 5 for which SE and SEP calculations have been performed [42,43].…”