Infrared spectroscopy of hydrated benzene cluster cations, [C6H6-(H2O)n]+ (n = 1–6): Structural changes upon photoionization and proton transfer reactions

Abstract

Infrared (IR) spectra of benzene-(water) n cluster cations (Bz-W n ) + (n ¼ 1-6) in the OH and CH stretching vibrational region were observed in order to investigate their structure and reactivity. The cluster cations were prepared by two different production methods: one is due to collision between bare benzene cations and water clusters; and the other utilizes resonance enhanced multiphoton ionization (REMPI) of neutral clusters. The former method prefers the production of the most stable isomer cluster cations, while the latter would reflect the Franck-Condon restriction in the ionization process. The structures of the n ¼ 1 and n ¼ 2 clusters were determined on the basis of the comparison between the IR spectra and density functional theory (DFT) calculations. In the n ¼ 1 cluster cation, the oxygen atom of the water molecule is located in the benzene ring plane and coordinates to the benzene moiety by two identical CH-O hydrogen bonds. The IR spectra of the n ¼ 2 cluster cation showed absorption bands arising from two different types of isomers: one has a hydrogenbonded water dimer interacting with the benzene cation; in the other isomer two water molecules are independently bound to the benzene cation. The production ratio between the isomers was found to strongly depend on the cluster ion preparation methods. Except for the case of the n ¼ 2 cluster, the cluster cations prepared by the two different methods gave identical IR spectra. This means that quite extensive rearrangements of the cluster structure occur upon ionization of the neutral clusters, leading to the most stable form of the cluster cations. The spectral features of the n ¼ 3 cluster cation are very similar to the n ¼ 2 cluster, suggesting similar structures among these clusters. Higher clusters larger than the n ¼ 3 cluster showed quite different IR spectra from those of the n 3 clusters, but their spectral features are very similar to those of hydrated clusters of protonated species, X-H + -(H 2 O) n , indicating that proton transfer reactions from the benzene cation to the water moiety occur in the larger clusters than those with n ¼ 3.

Structures and Dissociation Channels of Protonated Mixed Clusters around a Small Magic Number: Infrared Spectroscopy of ((CH3)3N)n–H+–H2O (n = 1–3)

“…Details of the experimental apparatus have been described elsewhere 29 and only brief description is given here. Protonated mixed clusters were produced by pulsed discharge of the TMA/H 2 O mixed vapor seeded in the Ar buffer gas (total pressure of 5 atm).…”

Electronic and vibrational spectra of protonated benzaldehyde-water clusters, [BZ-(H2O)n≤5]H+: Evidence for ground-state proton transfer to solvent for n ≥ 3

“…14,17,18 The latter scenario corresponds to the onset for the formation of an H-bonded solvent network. The global minimum structure corresponds to the cis-BZH + -(H 2 O) 2 structure, cw2-1, in which a H-bonded (H 2 O) 2 dimer binds to the OH proton of cis-BZH + in a linear fashion (Fig.…”

“…As the PA of (H 2 O) n clusters increases substantially with cluster size n (Table I), often intracluster proton transfer from AH + to the water solvent network occurs above a critical cluster size, n ≥ n c . 8,[14][15][16][17][18] Electronic excitation of AH + ions often has a drastic effect on the PA of A. As a consequence, excited state proton transfer to or from the solvent cluster may be triggered by electronic excitation depending on whether the PA of A decreases or increases upon electronic excitation.…”

Optimized structures and vibration frequencies of the ether–water complex: a DFT and FTIR study

“…Tanabe et al [4] investigated the O-H stretching vibrations of jet-cooled phenol and phenol-(H 2 O) n (n = 1-3) complexes by IR-UV double-resonance spectroscopy. Miyazaki et al [5] observed the infrared (IR) spectra of benzene-(water) n cluster cations (Bz-W n ) ? (n = 1-6) in the O-H and C-H stretching vibrational regions.…”

“…One example in the biological system is that intramolecular hydrogen bonding is partly responsible for the secondary, tertiary, and quaternary structures of proteins and nucleic acids. In particular, hydrogen-bonded organics-water clusters have been investigated intensively in recent years from the experimental and the theoretical points of view [2][3][4][5][6][7][8][9][10]. For instance, He et al [2,3] studied the water complexes of m-, p-, and o-aminobenzoic acid using two-color resonantly enhanced multiphoton ionization (REMPI) and UV-UV holeburning spectroscopy.…”