Chih-Kai Lin

• PhD
• PostDoc Position at Academia Sinica

In this work, we analyze the vibrational spectra of ammonium, methylammonium, and dimethylammonium ions solvated by either water molecules or bisulfate anions using anharmonic vibrational algorithms. Rich and complicated spectral features in the 2700-3200 cm-1 region of the experimental spectra of these clusters are attributed to originate from str...

The methylammonium ion (CH3NH3+, or noted as MA-H+) is one of the smallest organic ammonium ions that play important roles in organic-inorganic halide perovskites. Despite the simple structure, the vibrational spectra of MA-H+ exhibit complicated features in the 3 μm region which are sensitive to the solvation environment. In the present work, we h...

Intriguing vibrational features of solvated protonated methanol between 2400-3800 cm-1 are recorded by infrared predissociation spectroscopy. Positions of absorption bands corresponding to OH stretching modes are sensitive to changes in solvation environments, thus leading to changes in these vibrational features. Two anharmonic coupling mechanisms...

The appearance of multiple bands in the N–H stretching region of the infrared spectra of the neutral methylamine dimer and trimer is a sign of NH bend–stretch anharmonic coupling. Ab initio anharmonic calculations were carried out in a step-wise manner to reveal the origin of various bands observed in the spectrum of the methylamine dimer. A seven-...

Studies on the vibrational spectra of various ammonium-centered clusters under different solvation environments have raised interest over the last thirty years. The gas-phase infrared photodissociation spectroscopy (IRPD) experiments showed that these NH4+Xn clusters exhibit rich spectral features from 2600 to 3400 cm-1. In this work, we have simul...

Infrared spectra for a series of asymmetric proton‐bound dimers with protonated trimethylamine (TMA‐H⁺) as the proton donor were recorded and analyzed. The frequency of the N–H⁺ stretching mode is expected to red shift as the proton affinity of proton acceptors increases. The observed band, however, shows a peculiar splitting of approximately 300 c...

Huge Fermi resonance coupling was found in the experimental IR predissociation spectra of proton‐bound dimers based on protonated trimethylamine (TMA‐H⁺). An ab initio anharmonic vibrational analysis could explain the quasi‐two‐level behavior of the multiple states in the Fermi resonance as the proton affinity of proton acceptors varies. Abstract...

Strong coupling between stretching fundamentals and bending overtones of vibrational modes, known as Fermi resonance (FR), has been observed for proton motions in the protonated trimethylamine-water cluster. To investigate the role of FR, we examined the vibrational spectra of other three protonated ammonia/amine-water clusters, including the NH4+...

To model the collision-induced dissociation mass spectrometry (CID-MS) of Na⁺-tagged hexoses, it is not only required to perform an extensive sampling of the conformational space as addressed in our previous work [Huynh et al. Phys Chem Chem Phys 2018, 20 (29), 19614–19624]. It is also necessary to apply a sufficiently reliable quantum chemical met...

In this work, starting from the general theory of sum-frequency generation (SFG), we proposed a computational strategy utilizing density functional theory with periodic boundary conditions to simulate the vibrational SFG of molecules/solid surface adsorption system. The method has been applied to the CH3OH/TiO2(110) system successfully. Compared wi...

Based on atomic electronic configuration and Ti-Se coordination, a valence bond model for the layered transition metal dichalcogenide (TMDC) 1T -TiSe2 is proposed. 1T -TiSe2 is viewed being composed of edge-sharing TiSe4-plaquettes as TiSe2-ribbon chains in each layer via a directional valence shell electron distribution as chemical bonds, in contr...

Nitrogen is one of the most common heteroatom appearing in heterocyclic aromatic compounds (HACs) as well as the frequently applied dopant in graphene nanoflakes/nanoribbons. The pyridine moiety is an intuitive and stable common feature of these compounds; but interestingly, using density functional theory calculations, we found that the N-hydrogen...

In this reply to the comment on 'Oxygen vacancy-induced magnetic moment in edge-sharing CuO2 chains of ' (2017 New Journal of Physics 19 023206), we have clarified several key questions and conflicting results regarding the size of the intra-chain nearest neighbor coupling J 1 and the sign of the Weiss temperature Θ defined in the Curie–Weiss law o...

As nitrogen-doped graphene has been widely applied in optoelectronic devices and catalytic reactions, in this work we have investigated where the nitrogen atoms tend to reside in the material and how they affect the electron density and spectroscopic properties from a theoretical point of view. DFT calculations on N-doped hexagonal and rectangular...

The focus of this research is on the electron transfer and its reaction rate at the perovskite cathode of a photoelectrochemical cell for hydrogen production. By employing the density functional theory (DFT), the electron density, projected density of states (PDOS), electron distribution and electron transfer path between [Fe-Fe] hydrogenase and th...

Sum-frequency generation spectroscopy is a powerful tool for analysing molecular species and orientation configurations on a surface or an interface. In addition to conventional vibrational resonant techniques, the electronic resonant (electronic sum-frequency generation [ESFG]) ones have been developed recently. We have established the theoretical...

Li₂CuO₂ is a typical charge transfer insulator with CuO₂ chains that are composed of edge-shared CuO₄ plaquettes. The existence of oxygen vacancies for single crystals prepared under various oxygen partial pressures has been confirmed by the chemical and thermogravimetric analyses. The puzzling discovery...

We have established finite-sized model molecules of hexagonal graphene nanoflakes which consisted of up to about 400 carbon atoms and certain defects, and calculated their geometric structures, molecular orbitals and valence electron excitation properties by DFT and TD-DFT approaches. Several types of defects such as single nitrogen-atom dopants, v...

Following the surface enhanced Raman scattering (SERS), we shall investigate the possibility of observing surface-enhanced sum-frequency generation (SESFG), which refers to the transformation of ordinary vibrational SFG (i.e. singly resonant) into SESFG. Two mechanisms of SESFG will be studied; one is due to the transformation of singly-resonant vi...

Recent rapid progress in quantum chemical calculations has made it possible to perform the first principle calculations of various molecular spectroscopies and photophysical processes. Anharmonic effect on molecular electronic absorption and luminescence like fluorescence and phosphorescence spectroscopies and electronic relaxation processes like i...

The SFG technique has become popular since the pioneering work conducted by Shen's group in late 1980s. Combined the advantages of other surface-detecting techniques, the SFG technique could identify both chemical species and orientations adsorbed on surfaces or inserted between surfaces. In view of the recent tremendous experimental activities of...

Sum-frequency generation (SFG) spectroscopy is a powerful tool for not only identifying molecular species but also analyzing orientation configurations on a surface/interface. In this Article, we presented reformulation of the theoretical framework of electronic SFG spectroscopy, the signal of which could be greatly enhanced by tuning one or two in...

The b-hairpin is a building block in the β-sheet structure. Understanding the formation of the β-hairpin may provide insight into the formation of β-sheet structures in, for example, protein amyloids. In this study, we performed molecular dynamics (MD) simulations to investigate the temperature-dependent transition behaviors of the GB1 β-hairpin pe...

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...

In this paper, we introduce recent works on the mathematical treatments and the first-principle calculations concerning the internal conversion rates for the cases with anharmonic potentials, and conical intersecting potentials. The simulations of absorption and emission spectra with anharmonic effects are also presented to check the validity of th...

The density matrix method is a powerful theoretical technique to describe the ultrafast processes and to analyze the femtosecond time-resolved spectra in the pump-probe experiment. The dynamics of population and coherence of the system can be described by the evolution of density matrix elements. In this chapter, the applications of density matrix...

In this work geometric optimization and potential energy surface (PES) scan for the TiO2 molecule were carried out to find out possible stable structures by using quantum chemical calculations. The ground state (S0 1 1A1) has the only equilibrium with a symmetric bent structure, whereas the linear conformer is unstable. The first singlet excited st...

The geometric, energetic, and spectroscopic properties of the ground state and the lowest four singlet excited states of pyrazine have been studied by using DFT/TD-DFT, CASSCF, CASPT2, and related quantum chemical calculations. The second singlet nπ* state, (1)A(u), which is conventionally regarded dark due to the dipole-forbidden (1)A(u)←(1)A(g) t...

The electronic spectrum of a cold molecular beam of zirconium dioxide, ZrO(2), has been investigated using laser induced fluorescence (LIF) in the region from 17,000 cm(-1) to 18,800 cm(-1) and by mass-resolved resonance enhanced multi-photon ionization (REMPI) spectroscopy from 17,000 cm(-1)-21,000 cm(-1). The LIF and REMPI spectra are assigned to...

The spectra of symmetry-forbidden transitions and internal conversion were investigated in the present work. Temperature dependence was taken into account for the spectra simulation. The vibronic coupling, essential in the two processes, was calculated based on the Herzberg-Teller theory within the Born-Oppenheimer approximation. The approach was e...

We have carried out a close examination on the mathematical treatments and the first-principle computations concerning the vibronic transitions between the S(0)(1)A(1) and the S(1)(1)A(2) states of formaldehyde. The simulation of absorption spectrum was presented with peak intensities calculated according to vibronic-coupled transition dipole momen...

Theoretical calculations on electronic excitation energies and absorption cross sections of the H3 defect center in diamond were performed. We constructed model clusters with up to 180 atoms to imitate the local environment of the defect center and conducted first-principle calculations. TD-DFT predicted most accurately vertical excitation energy,...

The negatively charged nitrogen-vacancy defect center, (NV)(-), in diamond has been investigated theoretically for its one- and two-photon absorption properties involving the first excited state with the (3)A(2)-->(3)E transition. Time-dependent density functional theory (TD-DFT), configuration interaction with single excitation (CIS), and complete...

In this paper, we have studied the vibronic transitions between two symmetric double-well potentials by proposing a model Hamiltonian consisting of a harmonic oscillator and a parturition described by a Gaussian function that leads to a double minima potential with a barrier between the two energy minima. Making use of the contour integral form of...

In this paper we shall show how to calculate the single vibronic-level electron-transfer rate constant, which will be compared with the thermal averaged one. To apply the theoretical results to the dye-sensitized solar cells, we use a simple model to describe how we model the final state of the electron-transfer process. Numerical calculations will...

In studying ultrafast electron transfer from a dye molecule to a nanosized semiconductor particle, pump-probe experiments are commonly used. In this system the electron transfer (ET) rate is faster than vibrational relaxation so that the ET rate should be described by a single-level rate constant and the probing signal (often in the form of time-re...

In this work we shall show how to calculate the single vibronic- level electron transfer rate constant, which will be compared with the thermal averaged one. To apply the theoretical results to the dye- sensitized nano-crystalline semiconductor (Grätzel type) solar cells, we use a simple model to describe how we model the final state of the eletron...

Vibrational predissociation spectra of protonated water clusters H+(H2O)n, n = 9-11, are presented. Examination of the spectra in the free-OH stretching region revealed predominance of a single absorption band at approximately 3690 cm(-1) for three-coordinate H2O acting as a double-proton-acceptor/single-proton-donor in the n = 11 cluster. In contr...

This paper describes a systematic study on the clathrate structure of H+(H2O)21 using tandem mass spectrometry, vibrational predissociation spectroscopy, Monte Carlo simulations, and density functional theory calculations. We produced H+(H2O)n from a continuous corona-discharged supersonic expansion and observed three anomalies simultaneously at th...

The photodissociation of isotope-labeled toluene C(6)H(5)CD(3) and C(6)H(5)(13)CH(3) molecules at 6.4 eV under collision-free conditions was studied in separate experiments by multimass ion imaging techniques. In addition to the major dissociation channels, C(6)H(5)CD(3) --> C(6)H(5)CD(2) + D and C(6)H(5)CD(3) --> C(6)H(5) + CD(3), the respective p...

A constant momentum mass spectrometer with a two-dimensional ion detector in conjunction with a pulsed vacuum ultraviolet laser is used for the simultaneous measurement of the translational energy distributions of many different fragments. A description of the apparatus and its performance are presented. Preliminary experimental results on the phot...

The dissociation rate of benzene and d6-benzene were measured under collision-free condition by multimass ion imaging techniques. The value of 1±0.2×105 s−1 and 5±1×104 s−1 were obtained for benzene and d6-benzene, respectively, with internal energy of 618 kJ/mol. The dissociation rate of benzene with internal energy of 483 kJ/mol was too slow to b...

Vibrational predissociation spectra of protonated water clusters H 1 (H 2 O) n , n ¼ 9–11, are presented. Examination of the spectra in the free-OH stretching region revealed predominance of a single absorption band at B3690 cm À1 for three-coordinate H 2 O acting as a double-proton-acceptor/single-proton-donor in the n ¼ 11 cluster. In contrast, t...