Branching ratios in photodissociation of aniline-based hydrogen-bonded ternary cluster cations

Infrared (IR) predissociation of hydrogen-bonded ternary cluster ions such as aniline-water-ethanol (AWE(+)), aniline-water-isopropanol (AWP(+)), aniline-methanol-ethanol (AME(+)), aniline-water-pyrrole (AWPy(+)), and aniline-water-benzene (AWB(+)) was examined in the region of 2700-4000 cm(-1) to explore the key factors which determine the branching ratios in the concurrent unimolecular dissociation. The smaller solvent molecule was predominantly ejected when the binding energies of the two were not too different. On the other hand, when they were far off, the binding energy also acted significantly on the branching ratio. Besides, mode-selective IR predissociation was observed, while the selectivity was not quite distinct. The IR predissociation of ternary cluster ions bound via hydrogen bonding is considered to occur on a time scale much faster than intramolecular vibrational energy redistribution, which was proved by a statistical transition state theory.

Infrared predissociation reaction of the hydrogen bonds in the ternary cluster cation of aniline–water–benzene +

Observing and quantifying the like-charge attraction in liquids and solutions is still challenging. However, we showed that elusive cation-cation hydrogen bonding may govern the structure and interaction in hydroxyl-functionalized ionic liquids. Therefore, cationic cluster formation depends on the shape, charge distribution, and functionality of the ions. We demonstrated by means of solid-state 2H NMR spectroscopy that cationic clusters change the structure and dynamics of ionic liquids. With increasing alkyl chain length, we observed two deuteron quadrupole coupling constants for the OD groups, differing by about 30 kHz. The lower value was assigned to the cation-cation interaction, indicating that the average (c-c) hydrogen bonds are stronger than the (c-a) hydrogen bonds between the cation and the anion despite the repulsive and attractive Coulomb interaction in the first and latter cases. Ion mobility could be studied by 2H NMR spectroscopy, although the deuterons in the hydrogen-bonded clusters underwent fast exchange. Our results also showed that simple relaxation models are not applicable anymore and that anisotropic motion must be considered.

New ternary and quaternary molybdenum cluster chalcohalides were obtained by high-temperature reactions between Mo, chalcogens, and halogens in evacuated ampules. The crystal structures of [Mo3Se7(TeBr3)Br2]2[Te2Br10] (1), [Mo3Se7(TeI3)I2]I (2), and [Mo3Te7(TeI3)3]2(I)(TeI3) (3) were determined by single-crystal X-ray diffraction. The structures of 1 and 2 consist of positively charged zigzag chains infinity1 [Mo3Se7(TeX3)X4/2] (X=Br, I), with Te2Br102- and I-, respectively, as counterions. The TeI3- and TeBr3- ions function as bidentate ligands in 1 and 2. In 3, TeI3- is not coordinated to the metal but acts as a counterion to the [Mo3Te7(TeI3)3]+ cluster cation.

Control of photodissociation: vibrational mode selection and quantum interference

Spectroscopic studies of the hydrogen-bonding clusters of phenol were reviewed with an emphasis of the characterization of the cluster structures involving the proton transfer processes. Two experimental methods which were newly developed for the spectroscopy of the size selected clusters and their ions were described. Trapped ion photodissociation spectroscopy revealed that chromophore alternation occurs in the cluster cations with various proton-accepting molecules, such as NH3 and H2O. The infrared spectroscopy combined with the ionization detection was applied to the spectra of the OH vibrations which characterized the neutral clusters of phenol with water. The spectroscopic evidence of the ion-pair form of the neutral cluster is presented and the possibility of the intracluster acid-base reaction is discussed.

Inner-shell excitation spectra and fragmentation of small clusters of formic acid have been studied in the oxygen K-edge region by time-of-flight fragment mass spectroscopy. In addition to several fragment cations smaller than the parent molecule, we have identified the production of HCOOH.H+ and H3O+ cations characteristic of proton transfer reactions within the clusters. Cluster-specific excitation spectra have been generated by monitoring the partial ion yields of the product cations. Resonance transitions of O1s(C[double bond]O/OH) electrons into pi(CO)* orbital in the preedge region were found to shift in energy upon clusterization. A blueshift of the O1s(C[double bond]O)-->pi(CO)* transition by approximately 0.2 eV and a redshift of the O1s(OH)-->pi(CO)* by approximately 0.6 eV were observed, indicative of strong hydrogen-bond formation within the clusters. The results have been compared with a recent theoretical calculation, which supports the conclusion that the formic-acid clusters consist of the most stable cyclic dimer andor trimer units. Specifically labeled formic acid-d, HCOOD, was also used to examine the core-excited fragmentation mechanisms. These deuterium-labeled experiments showed that HDO+ was formed via site-specific migration of a formyl hydrogen within an individual molecule, and that HD2O+ was produced via the subsequent transfer of a deuterium atom from the hydroxyl group of a nearest-neighbor molecule within a cationic cluster. Deuteron (proton) transfer from the hydroxyl site of a hydrogen-bond partner was also found to take place, producing deuteronated HCOOD.D+ (protonated HCOOH.H+) cations within the clusters.

Spectroscopic information of ternary aniline clusters which include water has been obtained for the first time by infrared depletion spectroscopy. The vibrational spectra of the NH and OH stretching region of aniline−water−tetrahydrofuran (THF) clusters and their cations were measured by using infrared (IR) depletion spectroscopy. The infrared spectrum of the neutral cluster showed four absorption bands at 3715 cm-1 (free OH), 3491 cm-1 (free NH), 3403 cm-1 (bonded OH), and 3376 cm-1 (bonded NH). Analysis of the frequency red shifts of these bands showed that this cluster has a chainlike structure; the NH bond of aniline interacts with the oxygen atom of water, and one OH group of water interacts with the oxygen atom of THF. In contrast, the aniline cation acted as a double donor of hydrogen in the cluster cation. The infrared spectrum of the cluster cation showed three absorption bands at 3722 cm-1 (antisymmetric stretching of OH), 3636 cm-1 (symmetric stretching of OH), and 3230 cm-1 (bonded NH). Analysis of the red shifts of the infrared bands showed that the main interactions were the hydrogen bond between the NH bond of aniline and the oxygen atom of THF and that between the NH bonds of aniline and the oxygen atom of water.

Infrared (IR) and Raman spectroscopies involving ionization detection methods were applied for observing OH vibrations of size-selected phenol clusters. Also IR spectra of size-selected phenol cluster cations were observed by using IR multiphoton dissociation spectroscopy combined with an ion trapping technique. The cyclic form of the neutral phenol trimer was confirmed with experimental evidences. In the trimer cation, on the other hand, the IR spectrum shows that the cyclic form is no longer stable, but a chain form is feasible, in which all the phenyl moieties are bound by a single chain of hydrogen bonds. The drastic structure change induced upon ionization of the neutral trimer is discussed.

The intracluster proton transfer reaction occurring in the hydrogen-bonded cluster cations of phenol (C6H5OH) with water has been studied with trapped ion photodissociation (TIP) spectroscopy. Electronic spectra of [C6H5OH−(H2O)n]+ (n = 1−4) were observed in the region 380−400 nm, which reveals the chromophore of the cluster ions. It was found that the cluster ions of n ≤ 2 have the phenol ion (C6H5OH+) chromophore, while the n ≥ 3 cluster ions exhibit the phenoxy radical (C6H5O) chromophore, demonstrating that n = 3 is the critical size for intracluster proton transfer. Chromophore switching, occurring in the cluster ions of phenol with other solvent molecules as well as water, was discussed on the basis of the proton affinity of the solvent species. It was concluded that the intracluster proton transfer is a “push and pull” reaction determined only by the difference in the proton affinity between the phenoxy radical and the solvent molecules.

In the title compound, [CrBr(2)(C(5)H(14)N(2))(2)](2)Br(2).HClO(4).6H(2)O, there are two independent Cr(III) complex cations which are conformational isomers of each other. The Cr atoms lie respectively on a center of symmetry and on a mirror plane and have octahedral environments, coordinated by the N atoms of two 2,2-dimethylpropane-1,3-diamine ligands and by two Br atoms in trans positions. The Cr-N and Cr-Br bond lengths are in the ranges 2.078 (3)-2.089 (3) and 2.4495 (9)-2.5017 (9) A, respectively. The crystal structure consists of two Cr(III) complex cations, two Br(-) anions, a (ClO(4))(-) anion and an [H(13)O(6)](+) hydrogen-bonded cluster cation.

Electronic spectra of bare and hydrogen-bonded clusters of 2,6-difluoropyridine with water were observed in a supersonic free jet. The spectra indicate the existence of three isomers for 2,6-difluoropyridine-H 2 O 1:1 clusters. Ab initio molecular orbital calculations also support this result. The structures of the three clusters have hydrogen bonding between water hydrogen and nitrogen (N-site), water hydrogen and fluorine (F-site), and water oxygen and aromatic hydrogen (H-site). In the ground states of cluster cations, calculations suggest the existence of H-site cluster structure, and experiments also support these results. Following excitation into the D 0 state of the N-site cluster from the S, state, the cluster dissociates into bare 2,6-difluoropyridine and water, and the molecular orbital calculation also supports this result.

Fullerene molecules are affected and constrained by different interstellar environmental factors, such as UV radiation, atoms, and other coexisting molecules. To understand the coevolution of the interstellar fullerene chemistry, by tracking the accretion processes on fullerene cations, we present an investigation of the chemical reactivity of fullerene (C60) cations and smaller fullerene (C54/56/58) cations with hydrogen and C14H10 in the gas phase. Experiments are performed using a quadrupole ion trap in combination with time-of-flight mass spectrometry. The experimental results show hydrogenated fullerene-C14H10 cluster cations (i.e. [Hn C60(C14H10)m ]+ and [Hn C54/56/58(C14H10)m ]+) are efficiently formed through ion-molecule collision reaction. H-atoms are more likely to accumulate on the surface of fullerenes than C14H10; not only does hydrogen more easily form a covalent bond, the later accreted hydrogen will also expel the already accreted C14H10. Through theoretical calculations, we obtain the structure of newly formed clusters (e.g. [HC60(C14H10)]+ and [HC58(C14H10)]+) and the binding energies of their reaction pathways, together with IR spectra. The bonding ability plays a decisive role in the ternary cluster formation processes, and the existence of occupation and expulsion competitive reaction channels in the accretion processes on fullerene surfaces is confirmed. As part of the coevolution of the interstellar chemistry, the occupation and expulsion reaction modes should be considered when fullerenes further react with H-atoms and PAHs. As a result, the molecular structures of hydrogen/fullerene/PAH clusters are diverse, and hydrogenated-fullerene-related clusters (e.g. hydrogenated fullerenes or hydrogenated fullerenes-PAHs) have a higher distribution than non-hydrogenated-fullerene-related clusters (e.g. fullerenes or fullerenes-PAHs) in the interstellar environment.