Comparative FTIR spectroscopy of HX adsorbed on solid water: Ragout-jet water clusters vs ice nanocrystal arrays

In addition to revealing the stretch-mode bands of the smallest mixed clusters of HCl and HBr (HX) with water, the ragout-jet FTIR spectra of dense mixed water-acid supersonic jets include bands that result from the interaction of HX with larger water clusters. It is argued here that low jet temperatures prevent the water-cluster-bound HX molecules from becoming sufficiently solvated to induce ionic dissociation. The molecular nature of the HX can be deduced directly from the observed influence of changing from HCl to HBr and from replacing H2O with D2O. Furthermore, the band positions of HX are roughly coincidental with bands assigned to molecular HCl and HBr adsorbed on ice nanocrystal surfaces at temperatures below 100 K. It is also interesting that the HX band positions and widths approximate those of HX bound to the surface of amorphous ice films at <60 K. Though computational results suggest the adsorbed HX molecules observed in the jet expansions are weakly distorted by single coordination with surface dangling-oxygen atoms, on-the-fly trajectories indicate that the cluster skeletons undergo large-amplitude low-frequency vibrations. Local HX solvation, the extent of proton sharing, and the HX vibrational spectra undergo serious modulation on a picosecond time scale.     

Solvation states of HCl in mixed ether:acid crystals: a computational study

Acid solvation states are investigated in the recently discovered mixed ether:acid crystalline solids. The solids are simulated using on-the-fly molecular dynamics as implemented in the density functional code QUICKSTEP employing Gaussian basis sets. The solids are shown to display a remarkably broad range of acid solvation states, depending on the ether:acid ratio, including proton sharing in the 1:1 case, proton transfer to the ether in 1:2, and perturbed molecular acid in 1:6. The observed variation of the infrared spectra with the composition is accounted for qualitatively with the help of the calculations.     

Vibrational circular dichroism and absolute configuration of chiral sulfoxides: tert-butyl methyl sulfoxide

Mid-infrared vibrational unpolarised absorption and vibrational circular dichroism (VCD) spectra of CCl4 solutions of tert-butyl methyl sulfoxide (1) are reported. The spectra are compared to ab initio density functional theory (DFT) calculations carried out using two functionals, B3PW91 and B3LYP, and two basis sets, 6-31G* and TZ2P. The VCD spectra are calculated using Gauge-invariant atomic orbitals (GIAOs). The analysis of the VCD spectrum confirms the R(-)/S(+) absolute configuration of 1. The advantages and disadvantages of VCD spectroscopy in determining the absolute configurations of chiral sulfoxides are discussed.     

Determination of the absolute configuration of the sex pheromone of the obscure mealybug by vibrational circular dichroism analysis

Comparison of theoretical and experimental vibrational circular dichroism (VCD) spectra of an enantiopure synthetic sample of the obscure mealybug sex pheromone allowed the determination of the absolute configuration of the insect's pheromone.     

Spectroscopic and computational evidence for SO2 ionization on 128 K ice surface

The experimental part of this study focuses on FTIR spectroscopy of SO(2) adsorbate on the surface of ice nanoparticles at 128 K, in the 0.5-1 monolayer coverage range. In addition to the infrared spectroscopic features due to molecular SO(2), a structured band is observed at approximately 1030 cm(-1). A similar band was observed in past spectroscopic studies of SO(2) aqueous solutions, and assigned to anionic products of SO(2) ionization. Ab initio normal mode analysis of HSO(3)(-) yielded intense SO stretch bands in the vicinity of the observed "ionic" feature. The relative intensities of the molecular and the anionic bands indicate that 0.3 approximately 0.5 of the adsorbate is ionized. These results are consistent with the previously published data on isotopic exchange in SO(2)-covered ice nanoparticles (Devlin and Buch, J. Chem. Phys., 2007, 127, 091101) which pointed towards substantial SO(2) ionization at low temperatures. Density functional theory modeling of molecular and ionized adsorbate on a crystal ice slab suggests that anion solvation by molecular SO(2) adsorbate facilitates the SO(2) ionization process at the ice surface.