Paul L. Stiles

(HCN)m-Mn (M ) K, Ca, Sr): Vibrational Excitation Induced Solvation and Desolvation of Dopants in and on Helium Nanodroplets

Infrared (IR) laser spectroscopy is used to probe the rotational and vibrational dynamics of the (HCN)(m)-M(n) (M = K, Ca, Sr) complexes, either solvated within or bound to the surface of helium nanodroplets. The IR spectra of the (HCN)(m)-K (m = 1-3), HCN-Sr, and HCN-Ca complexes have the signature of a surface species, similar to the previously reported spectra of HCN-M (M = Na, K, Rb, Cs) [Douberly, G. E.; Miller, R. E. J. Phys. Chem. A 2007, 111, 7292.]. A second band in the HCN-Ca spectrum is assigned to a solvated complex. The relative intensities of the two HCN-Ca bands are droplet size dependent, with the solvated species being favored in larger droplets. IR-IR double resonance spectroscopy is used to probe the interconversion of the two distinct HCN-Ca populations. While only a surface-bound HCN-Sr species is initially produced, CH stretch vibrational excitation results in a population transfer to a solvated state. Complexes containing multiple HCN molecules and one Sr atom are surface-bound, while the nu(1) (HCN)(2)Ca spectrum has both the solvated and surface-bound signatures. All HCN-(Ca,Sr)(n) (n > or = 2) complexes are solvated following cluster formation in the droplet. Density-functional calculations of helium nanodroplets interacting with the HCN-M show surface binding for M = Na with a binding energy of 95 cm(-1). The calculations predict a fully solvated complex for M = Ca. For M = Sr, a 2.2 cm(-1) barrier is predicted between nearly isoenergetic surface binding and solvated states.

Infrared spectroscopy of the isomers of magnesium–HCN formed in helium nanodroplets: Comparisons with ab initio calculations

High-resolution infrared spectra are reported for two isomers of the magnesium–HCN binary complex, corresponding to the magnesium bonding at the nitrogen and hydrogen ends of the molecule. Stark spectra are also reported for these complexes, from which the corresponding dipole moments are determined. Ab initio calculations confirm that the potential energy surface has two minima, consistent with the experimentally determined structures. The wave functions of the two dimensional intermolecular coupled cluster singles doubles (triples) potential energy surface, calculated with the collocation method, are also reported for the magnesium–HCN system and are used to calculate the vibrationally averaged dipole moment for both isomers, which are then compared to experiment.

High-resolution infrared spectroscopy of Mg―HF and Mg―(HF)2 solvated in helium nanodroplets

High-resolution infrared (IR) spectroscopy is used to investigate the Mg-HF and Mg-(HF)(2) van der Waals complexes. Both complexes are formed and probed within helium nanodroplets. Rotationally resolved zero-field and Stark spectra are assigned to a linear binary complex composed of a Mg atom bound to the hydrogen end of the HF molecule. Although high level ab initio calculations predict a fluorine bonded complex, none of the observed IR bands can be assigned to this complex. The collocation method is employed to determine the bound states on the two-dimensional intermolecular Mg-HF potential energy surface. The ground and first excited state wave functions for this potential surface have zero amplitude in the well corresponding to the fluorine bonded complex, consistent with experiment. The two HF stretching bands of the Mg-(HF)(2) complex are observed and assigned using a combination of the spectral symmetry, ab initio calculations, pick-up cell pressure dependencies, and dipole moment measurements. Comparisons with the helium solvated HF dimer show large changes to the HF stretching frequencies upon the addition of a single Mg atom to the hydrogen side of (HF)(2).