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Wen Bih Tzeng

Bio: Wen Bih Tzeng is an academic researcher from Academia Sinica. The author has contributed to research in topics: Ionization & Ionization energy. The author has an hindex of 27, co-authored 130 publications receiving 2181 citations. Previous affiliations of Wen Bih Tzeng include Pennsylvania State University & United States Department of Energy.


Papers
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TL;DR: In this paper, a method of measuring the kinetic energy release arising from evaporative unimolecular dissociation is established; it employs a time-of-flight/reflectron to separate daughters and parents and enables the energy release to be determined from the peak shapes.
Abstract: The dissociation dynamics of protonated ammonia clusters is investigated following their production from neutrals using multiphoton ionization. A very useful method of measuring the kinetic energy release arising from evaporative unimolecular dissociation is established; it employs a time‐of‐flight/reflectron to separate daughters and parents and enables the energy release to be determined from the peak shapes. The method is found to lead to values of high precision. Using a modified statistical theory analysis suggested by Engelking, it is shown that binding energies for large cluster ions can be readily determined. The results compare very well with those derived by other methods, ones which generally have much more severe size limitations. In the case of (NH3)n H+, the observed drop in binding energy from n=5 to 6 is consistent with the particularly stable protonated pentamer structure. Heretofore, unavailable results are available from n=7 to 17, with hints of slightly more stable cluster ions at n=12...

87 citations

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TL;DR: In this paper, two-color resonant two-photon mass analyzed threshold ionization (MATI) spectroscopy was used to record the threshold ion spectra of deuterium-substituted isotopomers of aniline and p-fluoroaniline.
Abstract: Two-color resonant two-photon mass analyzed threshold ionization (MATI) spectroscopy was used to record the threshold ion spectra of deuterium-substituted isotopomers of aniline and p-fluoroaniline. The respective adiabatic ionization energies of C6H5NH2, C6H5NHD, C6H5ND2, C6D5NH2, C6D5NHD, C6D5ND2, p-FC6H4NH2, p-FC6H4NHD, and p-FC6H4ND2 were determined to be 62 271, 62 253, 62 233, 62 258, 62 237, 62 214, 62 543, 62 520, and 62 507 cm−1 with an uncertainty of about 5 cm−1. Analyses on the shifts in the electronic transition and ionization energies prove that the S1←S0 transition mainly occurs around the aromatic ring whereas the transition from the neutral S1 to the cationic state corresponds to the removal of one of the lone-pair electrons of nitrogen. The present results provide the first experimental evidence for the site-specific electronic transition in aniline as well as the isotope effects on the vibrations of the aniline cation. These findings are well supported by ab initio and density functiona...

73 citations

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TL;DR: In this article, a comparison of the S0 and S1 state vibrational modes is presented and discussed in terms of the changes in reduced masses, force constants, and mode mixing for aniline and its isotopic species.
Abstract: The structures and vibrations of C6H5NH2, C6H5NHD, C6H5ND2, C6D5NH2, C6D5NHD, and C6D5ND2 have been studied using ab initio molecular orbital (MO) calculations. Calculations at the CIS/6-31+G∗ level successfully predict that aniline is planar in the S1 state, and contracts along the long in-plane axis with a quinoid-like resonance structure. A comparison of the S0 and S1 state vibrational modes is presented and discussed in terms of the changes in reduced masses, force constants, and mode mixing for aniline and its isotopic species. The computed frequencies are found to be in very good agreement with the available experimental values.

67 citations

Journal ArticleDOI
TL;DR: In this article, the decay fractions of metastable ammonia cluster ions which undergo unimolecular (evaporative) dissociation in a time window of 1-40 μs were measured by using a reflection time-of-flight mass spectrometer.
Abstract: The decay fractions of metastable ammonia cluster ions which undergo unimolecular (evaporative) dissociation in a time window of 1–40 μs were measured by using a reflection time‐of‐flight mass spectrometer. Corrections concerning instrumental artifacts and ion trajectory of parents and daughters are made to imporve the precision of the measurements. The data are used to derive the Gspann parameter and heat capacity of clusters as described in evaporative ensemble model of metastable dissociation. Using the dissociation fractions measured in the present studies, in conjunction with kinetic energy release values previously measured in our laboratory, we apply Klots’ evaporative ensemble model to obtain binding energies of ammonia cluster ions (NH3)nH+, 4≤n≤17. The deduced binding energy values are found to be in very good agreement with both thermochemical data and Engelking’s modified statistical theory.

65 citations


Cited by
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TL;DR: The field of cluster research can trace its origins back to the mid-nineteenth century when early studies of colloids, aerosols, and nucleation phenomena were reported.
Abstract: The field of cluster research can trace its origins back to the mid-nineteenth century when early studies of colloids, aerosols, and nucleation phenomena were reported. The field underwent a resurgence of interest several decades ago when well-defined clusters were observed in supersonic expansions that could be investigated using mass spectrometers. The advent of the laser provided a new dimension, enabling detailed spectroscopic observations through the probing of systems of varying size and degree of solvation. Modern interest derives from recognition that interrogating clusters provides a way of studying the energetics and dynamics of intermediate states of matter as cluster systems evolve from the gas toward the condensed state. Herein, we endeavor to highlight some of the significant advances which have been made during the past several decades that have led to a nearly explosive growth of interest in the field of cluster science. Finally, we conclude that the field will continue to expand through i...

631 citations

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TL;DR: In this article, the rate coefficients and excess energies for dissociation, ionization, and dissociative ionization are presented for atomic and molecular species that have been identified or are suspected to exist in the atmospheres of planets, satellites (moons), comets, or as pollutants in the Earth atmosphere.
Abstract: Unattenuated solar photo rate coefficients and excess energies for dissociation, ionization, and dissociative ionization are presented for atomic and molecular species that have been identified or are suspected to exist in the atmospheres of planets, satellites (moons), comets, or as pollutants in the Earth atmosphere. The branching ratios and cross sections with resonances have been tabulated to the greatest detail possible and the rate coefficients and excess energies have been calculated from them on a grid of small wavelength bins for the quiet and the active Sun at 1 AU heliocentric distance.

603 citations

Journal ArticleDOI
TL;DR: A comprehensive review of the thermochemistry and its structural implications obtained from ab initio calculations will be presented, and relevant recent results from spectroscopy will be illustrated.
Abstract: 1.1. Historical Background Hydrogen bonds1,2 are one of the principal intermolecular forces. A special class are ionic hydrogen bonds (IHBs) that form between ions and molecules with bonds strengths of 5-35 kcal/mol, up to a third of the strength of covalent bonds. These strong interactions are critical, for example, in ionic clusters and nucleation, in electrolytes, ion solvation, and acid-base chemistry, in the structures of ionic crystals, surfaces, silicates, and clays, in surface adsorption, and in self-assembly in supramolecular chemistry and molecular crystals.3 IHBs are also important in bioenergetics including protein folding, enzyme active centers, formation of membranes and proton transport, and biomolecular recognition. With such wide-ranging roles, the fundamental properties of IHB interactions need to be understood. The energetics of IHB interactions cannot be isolated and quantified in the condensed phase. However, these interactions can be isolated and studied quantitatively in gas phase. These studies lead to a fundamental understanding of relations between IHB bond strengths and molecular structure, the solvation of ions, especially in the critical inner shells, and acid-based phenomena and bioenergetics. This review will present the basic insights that have been obtained in the past four decades. It will present a comprehensive review of the thermochemistry and its structural implications obtained from ab initio calculations. Relevant recent results from spectroscopy will be also illustrated. The advent of variable temperature high-pressure mass spectrometry (HPMS) introduced by Field and co-workers in the 1960s4 and pulsed high-pressure mass spectrometry (PHPMS) introduced by Kebarle in the late 1960s5 have been particularly significant. These workers realized that at pressures of several torrs and gas densities of 1016-1017 cm-3 in ion sources, ions can undergo 103-106 collisions with neutral molecules during typical residence times of 0.1-10 ms and establish thermal ion populations and * E-mail: m.mautner@solis1.com. 213 Chem. Rev. 2005, 105, 213−284

538 citations

Journal ArticleDOI

449 citations

Journal ArticleDOI
10 May 2013-Science
TL;DR: A universal temporal-phase formalism is introduced, mapping the Fano asymmetry parameter q to a phase ϕ of the time-dependent dipole response function, which uses quantum-phase control to amplify extreme-ultraviolet light resonantly interacting with He atoms.
Abstract: Symmetric Lorentzian and asymmetric Fano line shapes are fundamental spectroscopic signatures that quantify the structural and dynamical properties of nuclei, atoms, molecules, and solids. This study introduces a universal temporal-phase formalism, mapping the Fano asymmetry parameter q to a phase φ of the time-dependent dipole response function. The formalism is confirmed experimentally by laser-transforming Fano absorption lines of autoionizing helium into Lorentzian lines after attosecond-pulsed excitation. We also demonstrate the inverse, the transformation of a naturally Lorentzian line into a Fano profile. A further application of this formalism uses quantum-phase control to amplify extreme-ultraviolet light resonantly interacting with He atoms. The quantum phase of excited states and its response to interactions can thus be extracted from line-shape analysis, with applications in many branches of spectroscopy.

405 citations