Infrared Photodissociation Spectroscopy of [Aniline−(Water)_n]⁺ (n = 1−8):  Structural Change from Branched and Cyclic to Proton-Transferred Forms

Abstract

Infrared photodissociation spectra of [aniline-(H 2 O) n ] + (n = 1-8) are measured in the 2700-3800 cm-1 region. The spectra are interpreted with the aid of density functional theory calculations. The n = 1 ion has an N-H•••O hydrogen bond. The spectrum of the n = 2 ion demonstrates a large perturbation to both of the NH oscillators, indicating the 1-1 structure where each NH bond is bound to a water molecule. For the n = 3 ion, the calculated spectrum of the 2-1 branched structure coincides well with the observed one. For the n = 4 ion, there exist three strong bands at 2960, 3100, and 3430 cm-1 , and a very weak one at 3550 cm-1. The observed spectrum in the 3600-3800 cm-1 region is decomposed into four bands centered at 3640, 3698, 3710, and 3734 cm-1. The 2-2 branched isomer is responsible for all the features except the 3550 and 3710 cm-1 bands. These two bands are due to another isomer with a five-membered ring. An infrared band characteristic of the n = 5 ion appears at 3684 cm-1 , which is not seen in the spectra of the n = 1-4 ions. This band is indicative of a ring structure and assigned to the free OH stretching vibration of the three-coordinated (double-acceptor-single-donor

Vibrational predissociation of aniline(pyrrole)(water)2+ and aniline(pyrrole)(water)3+: Structures and dissociation dynamics

“…On the other hand, it shifted to red when either two or more hydrogen bonded water molecules were associated with N H of aniline in AnW 3 + or larger clusters; the symmetric NH 2 modes of AnW 3 + and AnW 4 + were observed at 3070 and 2960 cm −1 , respectively [18]. In case of AnPyW 2 + , the symmetric NH 2 stretching mode also showed Table 1 Zero point corrected energy, ZPCE (H), and relative energy (cm −1 ) of different possible structures for AnPyW2 + and AnPyW3 + , BSSE corrected binding energy, BE (eV) of different possible ejection channels calculated for the most probable structure of AnPyW2 + and AnPyW3 + .…”

“…According to Inokuchi et al [18], the symmetric NH 2 stretching mode of aniline was observed at ∼3105 cm −1 when one water molecule was bound to the N H of aniline via hydrogen bonding as they analyzed the structure of AnW n + (n = 1-8) cluster ions. On the other hand, it shifted to red when either two or more hydrogen bonded water molecules were associated with N H of aniline in AnW 3 + or larger clusters; the symmetric NH 2 modes of AnW 3 + and AnW 4 + were observed at 3070 and 2960 cm −1 , respectively [18].…”

“…Therefore, there is a red shift in N H stretching vibrational absorption for AnPyW 2 + . The gap between symmetric and asymmetric stretching NH 2 modes of solvated aniline ranges from 90 to 130 cm −1 when both N Hs of aniline are associated with two symmetric ligands [18], while it increases as much as twice or even more when asymmetrical ligands are bonded [15]. In Fig.…”

“…Many researchers reported experimental results on various solvated aniline systems employing infrared (IR) spectroscopy as well as bare aniline [8], taking advantage of its unsurpassed sensitivity to the presence of hydrogen bonding: dynamics [9], homo and hetero dimers [10][11][12][13], ternary clusters [14,15], and solvated aniline clusters with inert gas [16], water [17][18][19], methanol [17,20,21], N 2 , CH 4 , CHF 3 , and CO as solvents [22].…”

Photodissociation Dynamics of 4-Aminobenzonitrile+(Water)nClusters

“…[1][2][3][4][5][6][7][8][9][10][11] In particular, photofragmentation of electronically excited aniline + (water) n (An + W n ) clusters has been recently investigated to shed light on the intermolecular interaction between the amino group and water in the ionic state, where the average binding energies of water molecules with n = 5-20 were obtained and the optimized structures with n = 1-7 were suggested from the density functional theory (DFT) calculations.…”