Effect of argon environment on small water clusters in matrix isolation

Abstract

The influence of cryogenic argon environment on small water clusters was investigated by quantum-chemical simulation of structure and vibrational spectra of water clusters consisting of different numbers of molecules. Comparison of calculation results for vacuum and argon environment shows a red shift of spectral bands in argon. Obtained IR frequencies and intensities for water clusters in argon are compared with experimentally registered FTIR spectra of water trapped in a low-temperature argon matrix.

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

“…The (H 2 O) 4 cluster is held in the center of the [B 12 F 12 2– ] 8 polyhedron by coordination to four Li + ions centered on four of the six [B 12 F 12 2– ] 8 faces [Li–O = 1.995(1) Å] and by four relatively weak O–H···F hydrogen bonds [O­(H)···F = 2.951(2) Å]. The calculated most stable structure for an isolated (H 2 O) 4 cluster is cyclic and has a S 4 symmetry, ,, but the four O atoms in the calculated structures are coplanar. In contrast, the calculated structure of the cyclic (H 2 O) 4 cluster adsorbed to the NaCl(001) surface only has C 2 symmetry, as shown in Figure S12 .…”

“…The ν­(OH) and ν­(OD) stretching frequencies for Li 2 (H 2 O) 4 (B 12 F 12 ) and the isotopomers of its deuterated isotopologs are listed in Table , which also includes experimental ν­(OH) and ν­(OD) values assigned to cyclic (H 2 O) 4 or (D 2 O) 4 clusters in the gas phase, in liquid He droplets, and in noble gas matrices (see also Figures S1–S4). ,,,,,, It appears that the coordination of the tetramers to the Li + ions in Li 2 (H 2 O) 4 (B 12 F 12 ) and Li 2 (D 2 O) 4 (B 12 F 12 ) and does not significantly affect ν­(OH b ) and ν­(OD b ), respectively, relative to the gas phase or matrix isolated clusters. The main 3401 cm –1 ν­(OH b ) band for Li 2 (H 2 O) 4 (B 12 F 12 ) (fwhm 67 cm –1 ) is between the 3416 ν­(OH b ) band for the gas phase (H 2 O) 4 (fwhm 58 cm –1 ) and the 3383 ν­(OH b ) band for (H 2 O) 4 in a Ne matrix at 9 K. The main 2513 cm –1 ν­(OD b ) band for Li 2 (D 2 O) 4 (B 12 F 12 ) is within 21 cm –1 of the 2501 ν­(OD b ) band for the gas phase (D 2 O) 4 and the 2492 ν­(OD b ) band for (D 2 O) 4 in a Ne matrix at 7 K. There has been only one mixed-isotope cyclic water tetramer studied by IR spectroscopy prior to this work .…”

“…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 …”

“…The most important physicochemical methods for studying (H 2 O) n and M­(H 2 O) n m + clusters are vibrational spectroscopies, including Fourier transform infrared (FTIR), Raman, infrared molecular beam depletion, infrared sum frequency generation, infrared cavity ringdown, and terahertz laser vibration–rotation tunneling spectroscopies. ,,,− The number of ν­(OH) bands, their red shifts from H 2 O­(g), and their relative intensities, bandshapes, and bandwidths can suggest the value of n and provide information about the network of O–H···O hydrogen bonds in the cluster. Even when unambiguous assignments are not possible, FTIR spectra can generally rule out some compositions and/or structures …”

Solid-State NaBH4 Composites as Hydrogen Generation Material: Effect of Thermal Treatment of a Catalyst Precursor on the Hydrogen Generation Rate

“…The intense absorption at 1600-1700 cm −1 turned into a sharp symmetrical a.b. with the maximum shifted towards lower frequencies, indicating that the water molecules were isolated from each other [29]. Moreover, the number of a.b.…”