Papers by Michitoshi Hayashi
RSC Advances, 2020
This work shows that the natural oxygen defects in the CrI3 monolayer, a first 2D magnet, enrich ... more This work shows that the natural oxygen defects in the CrI3 monolayer, a first 2D magnet, enrich its structural, electronic, and magnetic properties, offering an effective way of tuning the functionality of CrI3 monolayer and other ultrathin magnets.
The Journal of Physical Chemistry A, 2002
The experiment for measuring doubly resonant infrared-visible (IR-vis) sum-frequency generation (... more The experiment for measuring doubly resonant infrared-visible (IR-vis) sum-frequency generation (SFG) has recently been developed by Shen and his co-worker and applied to Rhodamine 6G on silica surfaces. In this paper, based on the Born-Oppenheimer adiabatic approximation, a molecular theory for doubly resonant IR-vis SFG generation as a two-dimensional surface spectroscopy is presented. We shall show that this new nonlinear spectroscopy is closely related to IR and resonance Raman spectroscopy. In this preliminary theoretical derivation, the displaced harmonic potential energy surfaces model for the electronic ground and electronically excited states of the system are used to obtain the band shape functions for doubly resonant IR-vis SFG at a finite temperature. One of the unique and powerful abilities of this spectroscopy is that interference effects among IR-active modes can be observed. The calculated excitation profiles and IR spectra of the doubly resonant IR-UV SFG from Rhodamine 6G on fused silica are demonstrated. We shall show that this new nonlinear spectroscopy can provide experimentalists with access to microscopic properties of molecules on surfaces or at interfaces.
The journal of physical chemistry. B, Jan 25, 2016
THz absorption spectra of two polymorphs of diflunisal-form I and form III exhibit distinct THz a... more THz absorption spectra of two polymorphs of diflunisal-form I and form III exhibit distinct THz absorption features due to the influence of packing conformations on the frequency distributions and IR activities within 100 cm-1 region. In order to understand the origins of these THz modes, we perform a detailed mode analysis. The result shows that although the spectral features are different, these low-frequency phonon modes of the two molecular polymorphs have similar vibrational characteristics in terms of harmonic couplings between intermolecular and intramolecular vibrations.
Physical Review A, 2011
The collectivity of the electronic motion in finite systems is studied by using both the linear r... more The collectivity of the electronic motion in finite systems is studied by using both the linear response density functional theory (LRDFT) and the collectivity index defined by the transition density matrix. We demonstrate a collectivity analysis on the size-dependent peaks of electronic excitations of small sodium clusters (rings and linear chains). We find the excitation-mode dependence of the collectivity and large collectivities for the higher-energy plasmonic excitations. The collectivity analysis also clarifies the existence of the nondipolar collective motion at the energies very close to the higher-energy plasmonic excitations. The importance of the nondipolar motion is pointed out in light of nano-optics.
Journal of the Chinese Chemical Society, 2000
Starting from the von Neuman equation of quantum theoretical dynamics, by using the projection op... more Starting from the von Neuman equation of quantum theoretical dynamics, by using the projection operator technique, we write the generalised master equation (GME) of the reduced statistical operator. By using this technique we find a series expansion of the memory kernel which allows, in principle, a treatment of the higher orders of approximation. By keeping only the first term of this expansion, which corresponds to the second order of the perturbation treatment, GME is applied, in the Markov approximation, to the spin boson Hamiltonian to describe the dynamics of the relevant pseudo-spin subsystem. In the secular and rotating wave approximations this dynamics is found to be described by the Bloch equations.
We systematically investigate the possible complex transition origin of electronic excitations of... more We systematically investigate the possible complex transition origin of electronic excitations of giant molecular systems by using the recently proposed QNTO analysis [
The Journal of Physical Chemistry C, 2013
In this theoretical study, we aimed to simulate the sum-frequency generation (SFG) spectroscopy o... more In this theoretical study, we aimed to simulate the sum-frequency generation (SFG) spectroscopy of a thin polystyrene layer physically adsorbed on the graphene sheet and to figure out the orientation distribution of the phenyl units. To simplify the problem, we started the investigation by constructing molecular models with styrene and ethylbenzene monomers and styrene oligomers up to four units adsorbed on a finite-sized graphene hexagon. Geometric optimization results showed that the phenyl rings of the adsorbate always orientate close to the surface normal with a small tilt angle. The adsorption is weak but not negligible. SFG spectra have been simulated based on these calculated structures, vibrational frequencies, and dipole and polarizability derivatives to compare with experimental reports of polystyrene adsorbed on other surfaces.
The Journal of Physical Chemistry A, 2010
Conformation-dependent properties of L-phenylalanine in neutral and radical cations have been stu... more Conformation-dependent properties of L-phenylalanine in neutral and radical cations have been studied by using density functional theory (DFT) with a new density functional M05-2X, which is applicable to molecular systems with nonconvalent interactions. Adiabatic and vertical ionization energies and charge distributions in the cationic conformers in addition to optimized geometrical structures for both the neutral and the cationic conformers were evaluated. These results were compared with DFT (B3LYP) results. The M05-2X results can explain the correspondence between the observed and predicted conformers without ambiguity. The possibility of conformerization of neutral conformers is indicated from the results of IRC (intrinsic reaction coordinate) profiles.
The Journal of Physical Chemistry A, 2007
A molecular theory of time-resolved sum-frequency generation (SFG) has been developed. The theore... more A molecular theory of time-resolved sum-frequency generation (SFG) has been developed. The theoretical framework is constructed using the coupled-oscillator model in the adiabatic approximation. This theory can treat not only the vibrational spectroscopy but also vibrational dynamics. An application of this theory is also provided for estimation of the time constants of the intermolecular vibrational energy transfer between water molecules. This approach can be used for molecular analysis of the experimental results of Shen at al. on the SFG studies of vibrational dynamics of water.
Physical Review A, 1999
To explore the insights of recent experiments on the excitation of the NO molecule by chirped sub... more To explore the insights of recent experiments on the excitation of the NO molecule by chirped subpicosecond IR pulses, a corresponding theoretical study is presented. The agreements between experimental and theoretical results show the importance of the full-dimensional quantum-mechanical calculation.
Physical Review A, 2007
In recent experiments, highly charged molecular cations have been created by ultrashort high-powe... more In recent experiments, highly charged molecular cations have been created by ultrashort high-power laser pulses. In this paper, we theoretically study this process by the sequential model of molecular multiple ionization. Two examples-C 6 F 6 and C 6 H 6-are investigated. We calculate the product ratios, M 2+ / M + and M 3+ / M + ͑M =C 6 F 6 or C 6 H 6 ͒, and compare them with the experimental mass spectra. For C 6 F 6 , the calculated ratio M 2+ / M + agrees well with the experiment whereas the calculated M 3+ / M + is much greater than that of the measurement. This may suggest that heavy fragmentations take place at C 6 F 6 3+ cations. For C 6 H 6 , we predict a large amount of fragmentations at both C 6 H 6 2+ and C 6 H 6 3+ .
Physical Review A, 2005
In this paper, we demonstrate a detailed derivation of general analytical expressions of photoion... more In this paper, we demonstrate a detailed derivation of general analytical expressions of photoionization rates of spatially aligned large polyatomic molecules in the tunneling photoionization region. First, the molecular Coulomb-corrected Volkov function is derived for determining the continuum state, and the position dependence of the atoms forming the molecule is explicitly included in it. Second, using the molecular Coulombcorrected Volkov function, a Keldysh-type photoionization rate formula is derived. For this, a linear combination of atomic orbitals will be used for the initial state. The obtained photoionization rate formula shows that the molecular photoionization rate is the sum of the photoionization rates of the individual occupied orbitals of the atoms forming the molecule, which are modified by the position dependence of the atoms, and the quantum interference terms arising from the corresponding occupied orbitals of the constituent identical and different atoms. The formula explicitly indicates that the photoionization rate sensitively depends on the angle between the molecular axis and the polarization vector of the linearly polarized laser field, the internuclear distance, and the atomic ionization potential I by the expression exp͑2 ͱ 2mIF ជ • R ជ j / បF͒. This is a clear indication of the appropriateness of the formulas derived in this work since it is consistent with the experimental and numerical results obtained so far. Using the formula, we show numerical results of photoionization rates of all-trans polyacetylene radicals. In addition, from the formula is directly drawn the conclusion that the photoionization rate corresponding to the quantum interference terms is smaller when the distance between the atoms is longer in the case of laser polarization parallel to the molecular backbone.
Physical Review A, 1991
Mechanisms of intermolecular dephasings revealed in the time-resolved coherent anti-Stokes Raman ... more Mechanisms of intermolecular dephasings revealed in the time-resolved coherent anti-Stokes Raman scattering (CARS) spectra of a molecular ensemble are theoretically studied by deriving the microscopical expression for the scattered photon intensity averaged over the heat-bath variables. The intermolecular dephasing means the decay of the intermolecular coherence created by the pumping process, i.e. , a linear combination of the vibrational Raman transitions of the molecules at different sites. The intensity of the time-resolved CARS is expressed in terms of time-development matrix elements of the intermolecular coherence. An equation of motion for the intermolecular coherence is derived by using the projection operator method. The structure of the intermolecular-dephasing constant is clarified. The intermolecular-dephasing constant consists of the sum of population decay constants and the intermolecular pure dephasing constant that originates from an elastic interaction between the relevant molecules and a common heat-bath mode. The intermolecular pure dephasing constant is expressed in terms of the intramolecular pure dephasing constants and destructive interference of the intramolecular pure dephasings between the relevant two molecules. The intermolecular-dephasing constant is expressed as the sum of the intramolecular-dephasing constants of the relevant molecules when there is no common heat-bath mode. Inhomogeneous effects on the time-resolved CARS spectra are also investigated. A degree of the structural order is introduced to qualitatively express the inhomogeneity of local structures in the molecular ensemble. The microscopic expression derived in this paper has taken into account both incoherent and coherent optical processes in the thermally distributed molecular ensemble.
Physical Chemistry Chemical Physics, 2008
Quantum chemical calculations of the geometric structure, vertical excitation energies, and ioniz... more Quantum chemical calculations of the geometric structure, vertical excitation energies, and ionization potentials for the isomeric pair of 1,3-and 1,4-cyclohexadienes and their mono-and dications have been performed employing a variety of theoretical methods and basis sets. The computed ionization potentials and electronic excitation energies are used to evaluate the range of internal energies available for fragmentation of the cations following multiphoton resonance ionization of the cyclohexadienes in intense laser field. The conditions governing the competition between multiple ionization and decomposition of the ions are also discussed. Calculations of stationary points on the potential energy surfaces for various fragmentation channels and relative product yields at different available internal energies are then utilized to analyze the trends in branching ratios of major dissociation products of the 1,4-cyclohexadiene 2+ dication, which include C
Optical Materials, 2014
This report was cleared for public release by the USAF 88th Air Base Wing (88 ABW) Public Affairs... more This report was cleared for public release by the USAF 88th Air Base Wing (88 ABW) Public Affairs Office (PAO) and is available to the general public, including foreign nationals. Copies may be obtained from the Defense Technical Information Center (DTIC) (http://www.dtic.mil).
Nanoscale, 2013
The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) ... more The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L 3-edge X-ray absorption near-edge structure (XANES)/ extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt-C and Pt-N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-likeN doped CNTs.
Molecular Physics, 2005
2 þ 1 resonance-enhanced multiphoton ionization (REMPI) spectra of allene at 7.0-10.5 eV have bee... more 2 þ 1 resonance-enhanced multiphoton ionization (REMPI) spectra of allene at 7.0-10.5 eV have been observed. The excited vibronic symmetry has been determined from polarizationratio measurements. Based on the vibronic energies and peak intensities calculated using ab initio MO and time-dependent density functional theory, the very congested REMPI spectra have been assigned as due to p* p, 3p p, 4s p, 4p p, and 4d p transitions. Vibrational progressions related to the CH 2 twisting (4 s770 cm À1) have been observed for several excited electronic states. Calculated Franck-Condon factors also confirm that CH 2 twisting is the most active mode in the vibronic spectra of allene. In this study, theoretical calculations of two-photon intensities and polarization ratios have been made through the ab initio computed one-photon transition dipole moments to various electronic states as intermediates. As a starting point to interpret the complicated vibronic spectrum of allene, the theoretical approach, without vibronic couplings, has been applied to predict the peak positions, spectral intensities, and polarization ratios of Rydberg states, and qualitatively shows a considerable agreement with experimental observations.
Macromolecules, 2000
In a series of neutron reflectivity experiments, we studied the fundamental process of diblock fo... more In a series of neutron reflectivity experiments, we studied the fundamental process of diblock formation during reactive blending processes of an immiscible blend comprised of normal polysulfone (hPSU) containing 30% reactive end group-modified deuterated polysulfone (dPSU-R) and polyamide (PA). Diblock formation (dPSU-b-PA) and dPSU-R enrichment at the interface between the incompatible polymers were monitored in thin bilayer films using neutron reflectivity. These results are compared to experimental results obtained with bilayer films of pure nonreactive deuterated PSU (dPSU) and PA and pure reactive dPSU-R and PA, respectively. The interfacial width in the pure reactive system is slightly larger than that in the pure nonreactive system, indicating the formation of a diblock copolymer at the interface of the reactive system. The results for the diluted system (30% dPSU-R + 70% hPSU) show an enrichment of the deuterated species at the interface. The amount of dPSU-R at the interface rises from 30 vol % initially, up to an equilibrium value of 47 vol % after annealing at 210°C within about 30 min. This is interpreted as the formation of diblock copolymer out of the reactive components, dPSU-R and PA, as an interfacial reaction. Annealing at T) 210°C for substantially longer times reveals no further evolution of the interfacial profile, indicating that the diblock, once formed, stays localized at the interface. The formation of a diblock monolayer with complete coverage of the interfacial area is not observed. This is probably due to steric hindrance and strong segregation of the diblock between dPSU-R and PA. The block copolymer layer once formed at the interface suppresses the approach of additional dPSU-R homopolymer toward the interface due to the conformational entropy costs to the homopolymer and block copolymer already at the interface. For these reasons, it is possible to diminish but not eliminate the interfacial tension (γ > 0) between the PSU and PA, as it is not possible to build up a large enough normalized surface excess, z*/R g < 1, of dPSU-b-PA.
Journal of the American Chemical Society, 2012
Nonplanar chiral aromatic molecules are candidates for use as building blocks of multidimensional... more Nonplanar chiral aromatic molecules are candidates for use as building blocks of multidimensional switching devices because the π electrons can generate ring currents with a variety of directions. We employed (P)-2,2′-biphenol because four patterns of π-electron rotations along the two phenol rings are possible and theoretically determine how quantum switching of the π-electron rotations can be realized. We found that each rotational pattern can be driven by a coherent excitation of two electronic states under two conditions: one is the symmetry of the electronic states and the other is their relative phase. On the basis of the results of quantum dynamics simulations, we propose a quantum control method for sequential switching among the four rotational patterns that can be performed by using ultrashort overlapped pump and dump pulses with properly selected relative phases and photon polarization directions. The results serve as a theoretical basis for the design of confined ultrafast switching of ring currents of nonplanar molecules and further current-induced magnetic fluxes of more sophisticated systems.
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Papers by Michitoshi Hayashi