Infrared Spectroscopy of (HCl)_m(H₂O)_n Clusters in Helium Nanodroplets: Definitive Assignments in the HCl Stretch Region

Abstract

Infrared spectra in the HCl stretch region (2600-2900 cm(-1)) are presented for small, mixed (HCl)(m)(H(2)O)(n) clusters solvated in helium nanodroplets. Sharp bands associated with the Cl-H...Cl stretch vibrations in m:n = 1:1, 2:1, 2:2, and 3:1 clusters are superimposed on a broad background that increases in intensity as larger clusters are grown within the droplets. The broad background is determined to be partially due to mixed clusters with m > 3 and n > 2. The sharp bands are assigned to specific cluster compositions, m:n, via pick-up pressure dependence studies and optically selected mass spectrometry. Orientation of the clusters is achieved with the application of a large electric field to the laser/droplet beam interaction region. The intensity of each band is measured as a function of the applied field strength. Simulations of this electric field dependence based on ab initio calculations of permanent dipole moments and vibrational transition moment angles leads to definitive structural assignments for each sharp band. The 2:1 complex is cyclic, and a band associated with the 2:2 cluster is determined to arise from the nonalternating cyclic structure.

Infrared spectroscopy in superfluid helium droplets

“…In clusters larger than two to six particles, depending on the molecules, bands due to unique cluster sizes and/or structures often remain unresolved. Clusters featuring hydrogen bonding, such as (H 2 O) n [67,68,72,125], (NH 3 ) n [126], (HF) n [127], (HCl) n [128], (CH 3 OH) n [61,129], and (HCl) n -(H 2 O) n [130][131][132] are characterized by the formation of cyclic structures containing up to 6 molecular units, such as those obtained in water clusters [67], see Panel (a) in Figure 6. In He droplets, pre-formed cycles (e.g.…”

Hydrophilicity and Microsolvation of an Organic Molecule Resolved on the Sub‐molecular Level by Scanning Tunneling Microscopy

“…[13,14] However,the geometrical arrangement of the resulting solvation shells for example,f or the chloride ion is only known theoretically. [15][16][17] Solvation of organic molecules is even more complex because their spatial extend as well as the varying charge density of functional groups need to be considered. Consequently,they offer more potential attachment sites,w hich complicate the interpretation of spectra and increase the computational effort.…”

Communication: Infrared spectroscopy of salt-water complexes

“…Such an approach has recently been used to explore the HCl/H 2 O system by spectroscopic observation of HCl(H 2 O) n complexes. [7][8][9][10][11] With this method, it becomes possible to determine how the ion-pair evolves as the hydration number is changed. Indeed, with sufficient water molecules, the ions should separate into a SIP complex.…”