Umpei Nagashima

Intramolecular proton transfer in various electronic states of o-hydroxybenzaldehyde

Abstract Intramolecular proton transfer in various electronic states of o -hydroxybenzaldehyde (OHBA) has been investigated experimentally and theoretically. The stable molecular structure in the ground state of OHBA is an intramolecularly hydrogen-bonded closed conformer. The potential surface of the ground state has only one minimum, and no S 0 -state tautomer exists as a metastable state. In the first excited 1 (π, π*) state of OHBA, the intramolecular proton transfer takes place and an enol tautomer is formed. The deformation of the benzene skeleton plays an important role in the dynamic process in the first excited 1 (π, π*) state. In the second excited 1 (π, π*) state and the first and second ionic states of OHBA, the intramolecular proton transfer to yield the enol tautomer does not take place. These results are consistent with the explanation that the nodal plane of the wavefunction stabilizes the enol tautomer only in the first excited (π, π*) state. The observed behavior concerning proton transfer of various hydrogen-bonded molecules also can be explained similarly.

Enhanced stability of ion-clathrate structures for magic number water clusters

The near threshold vacuum‐UV photoionization of water clusters has been performed by using a resonance line emission of argon at 11.83 eV. The well‐known intensity anomaly at the cluster ion (H2O)21H+ is observed even in this threshold photoionization, for the first time, with very small excess energy. Structures for the water cluster ions (H2O)21H+ and (H2O)28H+ which exhibit enhanced structural stability (magic number), are presented based on Monte Carlo simulations as well as on the analogy of our previous study on the stability of the (H2O)20NH+4 ion. The Monte Carlo calculations are carried out at the temperatures of 200, 150, 100, and 50 K for the ionized water clusters (H2O)nH+ around n=21 and also around n=28, which includes the ionic hydrogen‐bond interactions between an H3O+ ion and neutral H2O molecules. The clusters (H2O)21H+ and (H2O)28H+ have greater binding energies per molecule than their neighbors although the enhancement of the latter is somewhat temperature dependent. The calculations s...

The S1(n, π*) states of acetaldehyde and acetone in supersonic nozzle beam: Methyl internal rotation and C=O out‐of‐plane wagging

Fluorescence excitation spectra of CH3CHO, CH3CDO, (CH3)2CO, and (CD3)2CO have been observed in an Ar supersonic nozzle beam. Vibrational analyses have been performed for vibronic bands in the region at wavelengths longer than 313 nm. The 0–0 bands of the S1(n, π*) states were located at 29 771, 29 813, 30 435, and 30 431 cm−1, respectively. The spectra could be analyzed taking the C=O out‐of‐plane wagging and the CH3 internal rotation as active modes. By fitting a double minimum potential function to the observed vibrational levels, it has been shown that these molecules are pyramidally distorted in the S1(n, π*) state with barrier heights to inversion of 541, 578, 468, and 480 cm−1, respectively. Similar analyses using the Mathieu function gave threefold potential functions for the methyl internal rotation with barrier heights to rotation of 691, 645, 740, and 720 cm−1 for CH3CHO, CH3CDO, (CH3)2CO, and (CD3)2CO, respectively. High resolution measurements of rotational envelopes have shown that the out‐o...

Overview of a performance evaluation system for global computing scheduling algorithms

While there have been several proposals of high-performance global computing systems, scheduling schemes for the systems have not been well investigated. The reason is difficulties of evaluation by large-scale benchmarks with reproducible results. Our Bricks performance evaluation system allows the analysis and comparison of various scheduling schemes in a typical high-performance global computing setting. Bricks can simulate various behaviors of global computing systems, especially the behavior of networks and resource scheduling algorithms. Moreover, Bricks is partitioned into components such that not only can its constituents be replaced to simulate various different system algorithms, but it also allows the incorporation of existing global computing components via its foreign interface. To test the validity of the latter characteristics, we incorporated the NWS (Network Weather Service) system, which monitors and forecasts global computing systems behavior. Experiments were conducted by running NWS under a real environment versus a Bricks-simulated environment, given the observed parameters of the real environment. We observed that Bricks behaved in the same manner as the real environment, and NWS also behaved similarly, making quite comparative forecasts under both environments.

Performance Evaluation Model for Scheduling in Global Computing Systems

Striking progress of network technology is enabling high performance global computing, in which computational and data resources in a wide-area network (WAN) are transparently employed to solve large-scale problems. Several high performance global computing systems, such as Ninf, NetSolve, RCS, Legion, and Globus, have already been proposed. Each of these systems proposes to effectively achieve high performance with some efficient scheduling scheme, whereby a scheduler selects a set of appropriate computing resources that solve the client’s computational problem. This paper proposes a performance evaluation model for effective scheduling in global computing systems. The proposed model represents a global computing system by a queuing network, in which servers and networks are represented by queuing systems. Verification of the proposed model and evaluation of scheduling schemes on the model showed that the model could simulate behavior of an actual global computing system and scheduling on the system effectively.

Photofragmentation of mono‐ and dichloroethylenes: Translational energy measurements of recoiling Cl and HCl fragments

Translational energy (Et ) spectra of Cl and HCl fragments from vinylchloride, trans‐dichloroethylene, cis‐dichloroethylene, and 1,1’‐dichloroethylene have been measured for the π*←π excitation at 193 nm. Et distribution and angular dependence of the Cl fragment indicate that the two‐center dissociation occurs in a time faster than a rotation period and the recoiling organic radical (the counter fragment) is highly vibrationally excited. In dichloroethylenes, the presence of a second channel producing Cl atoms has been confirmed and attributed to the dissociation from the lower (n,σ*) state through a (π,σ*) state. The Et distribution of HCl fragments is nonstatistical and found to converge to null population at an energy less than half of the total available energy. This convergence point coincides with the value of the local available energy for the elimination reaction (activation energy —ΔH0reaction ). The yield of HCl molecules relative to Cl atoms is estimated to be ∼1.1 for vinylchloride. High effic...

Ninf: A Network Based Information Library for Global World-Wide Computing Infrastructure

Ninf is an ongoing global network-wide computing infrastructure project which allows users to access computational resources including hardware, software and scientific data distributed across a wide area network. Ninf is intended not only to exploit high performance in network parallel computing, but also to provide high quality numerical computation services and accesses to scientific database published by other researchers. Computational resources are shared as Ninf remote libraries executable at a remote Ninf server. Users can build an application by calling the libraries with the Ninf Remote Procedure Call, which is designed to provide a programming interface similar to conventional function calls in existing languages, and is tailored for scientific computation. In order to facilitate location transparency and network-wide parallelism, Ninf metaserver maintains global resource information regarding computational server and databases, allocating and scheduling coarse-grained computation for global load balancing. Ninf also interfaces with the WWW browsers for easy accessibility.

Excited state enol‐keto tautomerization in salicylic acid: A supersonic free jet study

Excited state enol‐keto isomerization in salicylic acid (SA) monomer and dimer has been studied in a supersonic free jet expansion. Two carboxylic group rotamers of SA with significantly different photophysical properties are found in the expansion. Rotamer I, the major form of SA in the expansion, has an intramolecular hydrogen bond and can undergo excited state tautomerization reaction. Its S1 origin is at 335.34 nm. Single vibronic level emission spectra are dominated by progressions in OH stretching (3230 cm−1), and in‐plane bending of the carboxylic group (240 cm−1). The spectra appear to consist of two components, normal (UV) and tautomer (BLUE) emissions, even at the origin. The intensity of the BLUE relative to the UV emission depends on the vibronic state, rather than the excess vibrational energy between the origin and 1100 cm−1. The fluorescence decay time profiles for both the emission components of rotamer I are identical within ∼1 ns experimental time resolution. A nonradiative decay process...

Particle mesh Ewald method for three-dimensional systems with two-dimensional periodicity

Abstract A particle mesh Ewald method for calculating Coulomb interactions in three-dimensional (3D) systems with two-dimensional (2D) periodicity was developed. Computational efficiency and accuracy of this method were evaluated for a TIP3P water system with 2928 particles in a cubic box with 2D periodicity. The accuracy of this method for calculating Coulomb interactions is comparable to our previous method that uses Fourier integral. For calculations with maximum errors in the Coulomb force of 0.4– 20.0 kJ mol −1 nm −1 , the current method was up to five times faster than the previous method.

Magic numbers for water-ammonia binary clusters: Enhanced stability of ion clathrate structures

The formation of water–ammonia binary clusters (H2O)n(NH3)mH+ (q≲40, q=n+m), have been investigated employing a neutral supersonic nozzle expansion of premixed water–ammonia gas with molecular‐beam‐mass spectrometry. The analysis of the mass spectra reveals that the number of water‐rich clusters is greatly increased as the cluster size is increased. Mass spectroscopic evidence for the existence of enhanced structural stabilities (‘‘magic numbers’’) has been found at the protonated clusters (H2O)20(NH3)mH+ (m=1–6) and (H2O)27NH+4 . Considerations for the magic number stabilities are presented within the framework of ion clathrate (ion‐centered cage) structures. Monte Carlo simulations are also presented for ionized (protonated) clusters around n=20 and n=27 with m=1. The clusters (H2O)20NH+4 and (H2O)27NH+4 have greater binding energies per molecule than their neighbors, in agreement with the mass spectroscopic observations. The calculated structure for (H2O)20NH+4 also indicates the stability of pentagona...