D2O clusters isolated in rare-gas solids: Dependence of infrared spectrum on concentration, deposition rate, heating temperature, and matrix material

Abstract

The infrared absorption spectra of D2O monomers and clusters isolated in rare-gas matrices were systematically reinvestigated under the control of the following factors: the D2O concentration, deposition rate, heating temperature, and rare-gas species. We clearly show that the cluster-size distribution is dependent on not only the D2O concentration but also the deposition rate of a sample; as the rate got higher, smaller clusters were preferentially formed. Under the heating procedures at different temperatures, the cluster-size growth was successfully observed. Since the monomer diffusion was not enough to balance the changes in the column densities of the clusters, the dimer diffusion was likely to contribute the cluster growth. The frequencies of the bonded-OD stretches of (D2O)k with k = 2-6 were almost linearly correlated with the square root of the critical temperature of the matrix material. Additional absorption peaks of (D2O)2 and (D2O)3 in a Xe matrix were assigned to the species trapped in tight accommodation sites.

Vapor Adsorption Measurements with Two‐Dimensional Membranes

“…This was consistent with the microscopic observation of water nanodroplets formed at surface defects under ambient atmosphere [22] . Recently, D 2 O clusters were isolated in rare‐gas matrices, and their IRAS fingerprints were found to change with the cluster size [23] . As the hydrogen‐bonded OD stretching vibrations in the clusters appeared red‐shifted, we interpret our spectra to be associated with D 2 O agglomerates forming at the nanostructured surface of CNMs.…”

Room-Temperature FTIR Spectra of the Cyclic S4 (H2O)4 Cluster in Crystalline Li2(H2O)4(B12F12): Observation of B and E ν(OH) Bands and Coupling of Strong O–H···O and Weak O–H···F Vibrations

“…In some studies, higher-wavenumber shoulders can be seen on ν­(OH b ) or ν­(OD b ) bands assigned to S 4 (H 2 O) 4 or (D 2 O) 4 clusters in noble gas matrices or in the gas phase. Some examples are shown in Figures S1, S3, and S4. ,, Only in the cases of the gas phase IR cavity ringdown spectra of (D 2 O) 4 (Figure S4) and (H 2 O) 4 (Figure S16) were the shoulders explicitly attributed to ν­(OD b ) or ν­(OH b ) band splitting . However, the shoulder in the spectrum of (D 2 O) 4 was estimated to represent a band only 4 cm –1 higher than the main ν­(OD b ) band, not ca.…”

“…Combined with the fact that Li 2 (H 2 O) 4 (B 12 F 12 ) has no IR bands above 1500 cm –1 other than the bands associated with the H 2 O molecules [viz. ν­(OH) and δ­(HOH) vibrations], it is an ideal structural and spectroscopic model for the putative cyclic S 4 (H 2 O) 4 cluster that is, in part, the subject of refs − , , , , , , , − , , , , , , , , − . We herein report the first experimental vibrational spectroscopic evidence for cyclic (H 2 O) 4 tetramers with unambiguous compositions and structure, viz., the FTIR spectra of Li 2 (H 2 O) 4 (B 12 F 12 ), Li 2 (D 2 O) 4 (B 12 F 12 ), Li 2 (HOD)­(H 2 O) 3 (B 12 F 12 ), and Li 2 (HOD)­(D 2 O) 3 (B 12 F 12 ).…”

“…Chemists and physicists have studied small water clusters for decades. − This includes calculations of their structures, stabilities, and vibrational spectra by theorists and experimental vibrational spectroscopic studies of (H 2 O) n clusters in low-temperature matrices, generated by cold jet expansion, or confined in metal–organic frameworks or crystalline organic or inorganic compounds. − Reasons for studying (H 2 O) n clusters range from understanding cloud and ice formation as well as other atmospheric phenomena (including the radiation balance of the earth), a variety of biochemical processes, as a bridge from the gas phase to condensed phases, as a bridge from single-molecule adsorption to monolayer and bilayer adsorption of H 2 O to solid surfaces, , as models for bulk phenomena such as proton transport and solvation, and as an easily accessable experimental platform for studying isotope effects …”

“…Low-temperature matrix and cold jet expansion experiments cannot produce neutral (H 2 O) n clusters with a single value of n , so typical FTIR spectra in these experiments contain ν­(OH) bands due to a mixture of neutral (H 2 O) n clusters with, for example, n = 3–6. Five examples of spectra from the literature are shown in Figures S1–S4. ,,,, The assignment of bands to particular (H 2 O) n clusters is generally based on experimental vs calculated ν­(OH) band positions, relative intensities as a function of H 2 O content, bandshapes, and bandwidths (many of the experimental papers include calculated fundamental vibrational frequencies). ,,,,,,,, It is also possible that more than one water cluster isomer is present for some values of n (see, for example, Figure S1).…”