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Journal ArticleDOI

Infrared photodissociation spectroscopy of [Aniline-(Water)n]+ (n = 1-8): Structural change from branched and cyclic to proton-transferred forms

29 May 2003-Journal of Physical Chemistry A (American Chemical Society)-Vol. 107, Iss: 21, pp 4230-4237

AbstractInfrared photodissociation spectra of [aniline−(H2O)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, as well as 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 se...

Topics: Photodissociation (52%), Ion (51%), Infrared (51%), Hydrogen bond (51%), Spectroscopy (50%) more

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TL;DR: This paper will focus on the major areas of research initiated by the Yuan T. Lee group and how these studies stimulated and influenced others in what is currently a vibrant and growing field of ionic clusters.
Abstract: Beginning in the mid-1980s, a number of innovative experimental studies on ionic clusters emerged from the laboratory of Yuan T. Lee combining infrared laser spectroscopy and tandem mass spectrometry. Coupled with modern electronic structure calculations, this research explored many facets of ionic clusters including solvation, structure, and dynamics. These efforts spawned a resurgence in gas-phase cluster spectroscopy. This paper will focus on the major areas of research initiated by the Lee group and how these studies stimulated and influenced others in what is currently a vibrant and growing field.

85 citations

Journal ArticleDOI
Abstract: Infrared photodissociation spectra of [Mg·(H2O)1-4]+ and [Mg·(H2O)1-4·Ar]+ are measured in the 3000−3800 cm-1 region For [Mg·(H2O)1-4]+, cluster geometries are optimized and vibrational frequencies are evaluated by density functional theory calculation We determine cluster structures of [Mg·(H2O)1-4]+ by comparison of the infrared photodissociation spectra with infrared spectra calculated for optimized structures of [Mg·(H2O)1-4]+ In the [Mg·(H2O)1-3]+ ions, all the water molecules are directly bonded to the Mg+ ion The infrared photodissociation spectra of [Mg·(H2O)4]+ and [Mg·(H2O)4·Ar]+ show bands due to hydrogen-bonded OH stretching vibrations in the 3000−3450 cm-1 region In the [Mg·(H2O)4]+ ion, three water molecules are attached to the Mg+ ion, forming the first solvation shell; the fourth molecule is bonded to the first solvation shell As a result, the most stable isomer of [Mg·(H2O)4]+ has a six-membered ring composed of the Mg+ ion, two of the three water molecules in the first solvation sh

55 citations

Journal ArticleDOI
Abstract: Infrared spectra of [Mg · (H2O)1,2]+ and [Al · (H2O)1,2]+ are measured in the OH stretching region (3200–3800 cm−1). The spectra show the symmetric and asymmetric OH stretching bands of water molecules that are directly bound to the metal ions through metal–oxygen intermolecular bonds. In addition to these bands, the [Al · (H2O)2]+ ion has another band at 3714 cm−1. This band is assigned to the free OH stretching vibration of the [HO–Al–H]+ ion; the aluminum ion is inserted into the O–H bond of one water molecule in [Al · (H2O)2]+.

50 citations

Journal ArticleDOI
TL;DR: The potential of the ABN(+)-H2O dimer is characterized in detail and supports the cluster growth derived from the IRPD spectra, and the formation of a solvent network stabilized by strong cooperative effects is favored over interior ion hydration which is destabilized by noncooperative effects.
Abstract: Infrared photodissociation (IRPD) spectra of mass-selected 4-aminobenzonitrile-(water)n cluster cations, ABN+-(H2O)n with n ≤ 4, recorded in the N–H and O–H stretch ranges are analyzed by quantum chemical calculations at the M06-2X/aug-cc-pVTZ level to determine the evolution of the initial microhydration process of this bifunctional aromatic cation in its ground electronic state. IRPD spectra of cold clusters tagged with Ar and N2 display higher resolution and allow for a clear-cut structural assignment. The clusters are generated in an electron impact source, which generates predominantly the most stable isomers. The IRPD spectra are assigned to single isomers for n = 1–3. The preferred cluster growth begins with sequential hydration of the two acidic NH protons of the amino group (n = 1–2), which is followed by attachment of secondary H2O ligands hydrogen-bonded to the first-shell ligands (n = 3–4). These symmetric and branched structures are more stable than those with a cyclic H-bonded solvent network. Moreover, in the size range n ≤ 4 the formation of a solvent network stabilized by strong cooperative effects is favored over interior ion hydration which is destabilized by noncooperative effects. The potential of the ABN+-H2O dimer is characterized in detail and supports the cluster growth derived from the IRPD spectra. Although the N–H bonds are destabilized by stepwise microhydration, which is accompanied by increasing charge transfer from ABN+ to the solvent cluster, no proton transfer to the solvent is observed for n ≤ 4.

26 citations

Journal ArticleDOI
Abstract: Microhydrated fluorobenzene cation clusters, C 6 H 5 F + –(H 2 O) n with n = 1 and 2, were characterized by IR photodissociation spectra in the O–H stretch range and UB3LYP/6-31G* calculations. The intermolecular C 6 H 5 F + –H 2 O potential features several minima with charge–dipole orientation and comparable binding energies ( D 0 ∼ 9 ± 1 kcal/mol). The C 6 H 5 F + –H 2 O spectrum is consistent with a structure in which the O atom of H 2 O approaches the C 6 H 5 F + cation from above the aromatic plane. The C 6 H 5 F + –(H 2 O) 2 spectrum reveals the presence of two isomers, in which either a (H 2 O) 2 dimer or two single H 2 O ligands are attached to C 6 H 5 F + . The detected C 6 H 5 F + –(H 2 O) 1,2 complexes were unreactive with respect to nucleophilic substitution.

25 citations

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Journal ArticleDOI
Abstract: The gas phase infrared spectra of the hydrated hydronium cluster ions H3O+·(H2O)n(n=1, 2, 3) have been observed from 3550 to 3800 cm^−1. The new spectroscopic method developed for this study is a two color laser scheme consisting of a tunable cw infrared laser with 0.5 cm^−1 resolution used to excite the O–H stretching vibrations and a cw CO2 laser that dissociates the vibrationally excited cluster ion through a multiphoton process. The apparatus is a tandem mass spectrometer with a radio frequency ion trap that utilizes the following scheme: the cluster ion to be studied is first mass selected; spectroscopic interrogation then occurs in the radio frequency ion trap; finally, a fragment ion is selected and detected using ion counting techniques. The vibrational spectra obtained in this manner are compared with that taken previously using a weakly bound H2 "messenger." A spectrum of H7 O + 3 taken using a neon messenger is also presented. Ab initio structure and frequency predictions by Remington and Schaefer are compared with the experimental results.

444 citations

Journal ArticleDOI
Abstract: Protonated water clusters, H+(H2O)n (n = 5−8), from a supersonic expansion have been investigated by vibrational predissociation spectroscopy and ab initio calculations. The experimental spectra were obtained at an estimated cluster temperature of 170 ± 20 K. Recorded absorption bands at the frequency range of 2700−3900 cm-1 are attributed to the free- and hydrogen-bonded-OH stretches of the ion core and the surrounding solvent molecules. Ab initio calculations, performed at the B3LYP/6-31+G* level, indicate that geometries of the H+(H2O)5-8 isomers are close in energy, with the excess proton either localized on a single water molecule, yielding H3O+(H2O)n-1, or equally shared by two molecules, yielding H5O2+(H2O)n-2. Systematic comparison of the experimental and computed spectra provides compelling evidence for both cases. The unique proton-transfer intermediate H5O2+(H2O)4 was identified, for the first time, by its characteristic bonded-OH stretching absorptions at 3178 cm-1. The existence of five-membe...

295 citations

Journal ArticleDOI
Abstract: The NH4+(H2O)3-6 cluster ions synthesized by a free jet expansion contain a variety of structural isomers. This investigation identifies some of these isomers by employing vibrational predissociation spectroscopy (VPS) in conjunction with ab initio calculations. The NH4+(H2O)n ions are produced by corona discharge of NH3/H2O seeded in a H2 beam. They are mass-selected and then vibrationally cooled in an octopole ion trap for infrared spectroscopic measurements. In the VPS, four distinct stretching vibrations (hydrogen-bonded and non-hydrogen-bonded NH and OH) are closely examined. The characteristic absorptions of these stretches, together with systematic temperature dependence measurements of their band intensities, allow us to identify both cyclic and noncyclic isomers in the supersonic jet. Such identification is corroborated by ab initio calculations performed at the B3LYP and MP2 levels using the 6-31+G* basis set. The satisfactory agreement in both vibrational frequencies and absorption intensities ...

99 citations

Journal ArticleDOI
Takahiro Sawamura1, Asuka Fujii1, Shin Sato1, Takayuki Ebata1, Naohiko Mikami1 
Abstract: OH stretching vibrations of hydrogen-bonded cluster ions of phenol (PhOH), [PhOH−(H2O)n]+ (n = 1−4), (PhOH)2+, and (PhOH−methanol)+ have been observed with infrared photodissociation spectroscopy in combination with an ion-trapping technique. Cluster ions were efficiently generated by ionization of phenol followed by a jet expansion and were mass-selectively stored by the radio frequency ion trap method, which allows us to observe infrared multiphoton dissociation yield spectra of size-selected cluster ions. For [PhOH−(H2O)n]+, the OH stretching vibrations of the water moieties strongly suggested that the n ≥ 3 cluster ions exhibit the proton-transferred form, [PhO−H3O+(H2O)n-1], while the n = 1 and 2 ions are of the nontransferred form, [PhOH+−(H2O)n]. As for (PhOH)2+, the infrared spectra indicate that the dimer ion is characterized as the open form, in which the phenol ion acts as a proton donor and the neutral phenol as an acceptor through their single hydrogen bond. The similar open form is also foun...

83 citations

Journal ArticleDOI
Abstract: The infrared spectra of (phenol)(H2O)n+ cluster ions (n = 1−4, 7, 8) have been recorded in the region from 2850 to 3800 cm-1. The method developed for this study (IR-PARI = infrared photodissociation after resonant ionization) allows sensitive IR spectroscopy of cluster ions from size-selected neutral precursors. The three-color laser scheme used for ion selection and dissociation consists of a two-color S0 → S1 → D0 ionization of a mass-selected cluster followed by IR photodissociation of the cluster ion. The IR spectra were taken by monitoring the photodissociation dip of the parent ion signal and by recording the rise of the −H2O fragment signal. The experimentally observed frequencies are compared to the results of ab initio calculations. No proton transfer is observed for the (phenol)(H2O)1,2+ clusters. In contrast to the S0 state, the structure of (phenol)(H2O)2+ turns out to be linear. In the case of the (phenol)(H2O)3,4+ clusters, linear and solvated structures are discussed. Within the solvated s...

80 citations