Mitchio Okumura

Bio: Mitchio Okumura is an academic researcher from California Institute of Technology. The author has contributed to research in topics: Spectroscopy & Infrared spectroscopy. The author has an hindex of 33, co-authored 102 publications receiving 4426 citations. Previous affiliations of Mitchio Okumura include University of California & University of California, Berkeley.

Vibrational spectroscopy of the hydrated hydronium cluster ions H3O+·(H2O)n (n=1, 2, 3)

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.

Lifetimes, spectra, and quenching of the excited states of polypyridine complexes of iron(II), ruthenium(II), and osmium(II)

Abstract: The lifetimes of the excited states formed by 530-nm excitation of polypyridine complexes of iron(II) (FeL/sub 3//sup 2 +/) and osmium(II) (OsL/sub 3//sup 2 +/) have been determined by laser flash-photolysis techniques. The FeL/sub 3//sup 2 +/ lifetimes, measured in water at room temperature using picosecond absorption spectrometry, are as follows (L,tau +- sigma(ns)):2,2',2''-terpyridine (2.54 +- 0.13); 2,2'-bipyridine (0.81 +- 0.07); 4,4'-dimethyl(2,2'-bipyridine) (0.76 +- 0.04); 1,10-phenanthroline (0.80 +- 0.07); 4,7-(diphenyl sulfonate)-1,10-phenanthroline (0.43 +- 0.03). Lifetimes for the analogous complexes of osmium(II) lie in the range 10-100 ns under the same conditions. Unlike the excited states of Ru(bpy)/sub 3//sup 2 +/ and Os(bpy)/sub 3//sup 2 +/ (lambda/sub max/430-460 nm, epsilon approx. 5 x 10/sup 3/ M/sup -1/ cm-/sup 1/), the excited state of Fe(bpy)/sub 3//sup 2 +/ does not luminesce or absorb significantly in the visible (epsilon < 10/sup 3/ M/sup -1/ cm/sup -1/ at lambda greater than or equal to 350 nm) but does exhibit intense absorption below approx. 325 nm. Rate constants for the quenching of the excited states of polypyridine complexes of osmium(II) and ruthenium(II) by ground-state polypyridine complexes of iron(II), ruthenium(II), and osmium(II) are reported and are ascribed to either electron-transfer or energy-transfer processes. The excited statesmore » of tris(2,2'-bipyridine)iron(II) and of bis(2,2',2''-terpyridine)iron(II) undergo reaction with Fe/sub aq//sup 3 +/ (0.5 M H/sub 2/SO/sub 4/, 25/sup 0/C) with a rate constant less than or equal to 1 x 10/sup 7/ M-/sup 1/ s/sup -1/. Based on a comparison of its properties with those of the luminescent charge-transfer excited states of ruthenium(II) and osmium(II) polypyridine complexes the excited state of FeL/sub 3//sup 2 +/ is identified as a ligand-field state.« less

Infrared spectra of the solvated hydronium ion: Vibrational predissociation spectroscopy of mass-selected H3O+.cntdot.(H2O)n.cntdot.(H2)m

Abstract: Infrared spectra of the mass-selected clusters H{sub 3}O{sup +}{sm bullet}(H{sub 2}O){sub n}{sm bullet}(H{sub 2}) and H{sub 3}O{sup +}{sm bullet}(H{sub 2}){sub n} (n = 1,2, and 3) were observed by vibrational predissociation spectroscopy The clusters were mass-selected and then trapped in a radio frequency ion trap Cluster dissociation by loss of H{sub 2} followed excitation of OH or H{sub 2} stretches Spectra were recorded by detecting fragment ions as a function of laser frequency From spectra of H{sub 3}O{sup +}{sm bullet}(H{sub 2}O){sub n}{sm bullet}(H{sub 2}), the authors were able to determine the spectrum of the hydrated hydronium ion H{sub 3}O{sup +}{sm bullet}(H{sub 2}O){sub n}, because the H{sub 2} formed weak complexes with the hydrates Spectra in the OH stretching region (3,000-4,000 cm{sup {minus}1}) were observed at a resolution of 13 cm{sup {minus}1} for clusters n = 1,2, and 3 The structure of the clusters and the perturbing effect of the H{sub 2} were inferred from a comparison with recent unpublished ab initio vibrational frequencies calculated by Remington and Schaefer

Infrared spectra of the cluster ions H7O+3⋅H2 and H9O+4⋅H2

Abstract: Infrared spectra of hydrated hydronium ions weakly bound to an H2 molecule, specifically H7O + 3 ·H2 and H9O + 4 ·H2, have been observed. Mass-selected parent ions, trapped in a radio frequency ion trap, are excited by a tunable infrared laser; following absorption, the complex predissociates with loss of the H2, and the resulting fragment ions are detected. Spectra have been taken from 3000 to 4000 cm^−1, with a resolution of 1.2 cm^−1. They are compared to recent theoretical and experimental spectra of the hydronium ion hydrates alone. Binding an H2 molecule to these clusters should only weakly perturb their vibrations; if so, our spectra should be similar to spectra of the hydrated hydronium ions H7O + 3 and H9O + 4 .

Vibrational Spectroscopy of the Cl.(H2O)n Anionic Clusters, n = 1-5

Abstract: The hydrogen-bonded and free OH stretch modes of Cl-(H2O)n (n = 1−5) have been observed by vibrational predissociation spectroscopy in the 2.6−3.2 μm region. Besides demonstrating that all clusters form strong ionic hydrogen bonds, the spectra provide clear evidence of water−water hydrogen-bonding networks in n = 4 and n = 5, with the broad spectrum of n = 5 resembling that of large neutral water clusters. No water−water hydrogen bonding is seen in n = 2 and n = 3, but these clusters appear to be solvated asymmetrically. While the data suggest that Cl- ion is solvated on the surface of water clusters, there are discrepancies between the observed spectra and ab initio predictions. This disagreement may stem from either zero-point motion or high cluster temperature, which tend to disrupt hydrogen bonding among the waters.

Bond Dissociation Energies of Organic Molecules

Abstract: In this Account we have compiled a list of reliable bond energies that are based on a set of critically evaluated experiments. A brief description of the three most important experimental techniques for measuring bond energies is provided. We demonstrate how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.

Bond dissociation energies of organic molecules

Abstract: In this Account we have compiled a list of reliable bond energies that are based on a set of critically evaluated experiments. A brief description of the three most important experimental techniques for measuring bond energies is provided. We demonstrate how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.