Coauthored Publications with: Tsai

Journal Article

Wu, C-C, Lin H-C, Chang Y-B, Tsai P-Y, Yeh Y-Y, Fan H, Lin K-C, Francisco JS.  2011.  Br 2 molecular elimination in photolysis of (COBr) 2 at 248 nm by using cavity ring-down absorption spectroscopy: A photodissociation channel being ignored. Journal of Chemical Physics. 135, Number 23 AbstractWebsite

A primary dissociation channel of Br 2 elimination is detected following a single-photon absorption of (COBr) 2 at 248 nm by using cavity ring-down absorption spectroscopy. The technique contains two laser beams propagating in a perpendicular configuration. The tunable laser beam along the axis of the ring-down cell probes the Br 2 fragment in the B 3Π + ou-X 1Σ g + transition. The measurements of laser energy- and pressure-dependence and addition of a Br scavenger are further carried out to rule out the probability of Br 2 contribution from a secondary reaction. By means of spectral simulation, the ratio of nascent vibrational population for v = 0, 1, and 2 levels is evaluated to be 1:(0.65 ± 0.09):(0.34 ± 0.07), corresponding to a Boltzmann vibrational temperature of 893 ± 31 K. The quantum yield of the ground state Br 2 elimination reaction is determined to be 0.11 ± 0.06. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state (COBr) 2 via internal conversion. A four-center dissociation mechanism is followed synchronously or sequentially yielding three fragments of Br 2 + 2CO. The resulting Br 2 is anticipated to be vibrationally hot. The measurement of a positive temperature effect supports the proposed mechanism. © 2011 American Institute of Physics.
Palazzetti, F, Tsai P-Y, Lombardi A, Nakamura M, Che D-C, Kasai T, Lin K-C, Aquilanti V.  2013.  Aligned molecules: Chirality discrimination in photodissociation and in molecular dynamics. Rendiconti Lincei. 24:299-308., Number 3 AbstractWebsite

Emergence of biochemical homochirality is an intriguing topic, and none of the proposed scenarios has encountered a unanimous consensus. Candidates for naturally occurring processes, which may originate chiral selection, involve interaction of matter with light and molecular collisions. We performed and report here: (1) simulations of photodissociation of an oriented chiral molecule by linearly polarized (achiral) light observing that the angular distribution of the photofragments is characteristic of each enantiomer and both differ from the racemic mixture; and (2) molecular dynamics simulations (elastic collisions of oriented hydrogen peroxide, one of the most simple chiral molecules, with Ne atom) demonstrating that the scattering and the recoil angles are specific of the enantiomeric form. The efficacy of non-chiral light (in the case of photodissociation) and of non-chiral projectile (in the case of collisions) is due to the molecular orientation, as an essential requirement to observe chiral effects. The results of the simulations, that we report in this article, provide the background for the perspective realization of experiments which go beyond the well-documented ones involving interaction of circularly polarized laser (chiral light) with the matter, specifically by making use of non-chiral, i.e. linearly polarized or unpolarized light sources, and also by obtaining chiral effects with no use at all of light, but simply inducing them by molecular collisions. The case of vortices is discussed in a companion paper. © 2013 Accademia Nazionale dei Lincei.
Liu, Y-T, Tsai M-T, Liu C-Y, Tsai P-Y, Lin K-C, Shih YH, Chang AHH.  2010.  Photodissociation of gaseous acetyl chloride at 248 nm by time-resolved fourier-transform infrared spectroscopy: The HCl, CO, and CH2 product channels. Journal of Physical Chemistry A. 114:7275-7283., Number 27 AbstractWebsite

In one-photon dissociation of gaseous acetyl chloride at 248 nm, time-resolved Fourier-transform infrared emission spectroscopy is used to detect the fragments of HCl, CO, and CH2 in the presence of Ar or O 2. The high-resolution spectra of HCl and CO are analyzed to yield the corresponding internal energy deposition of 8.9 ± 1.1 and 6.2 ± 0.9 kcal/mol. The presence of the CH2 fragment is verified by detecting the CO2 product resulting from the reaction of CH 2 and the added O2. The probability of the HCl formation via a hot Cl reaction with the precursor is examined to be negligible by performing two experiments, the CH3COCl pressure dependence and the measurement of Br2 with Cl reaction. The HCl elimination channel under the Ar addition is verified to be slowed by 2 orders of magnitude, as compared to the Cl elimination channel. The observed fragments are proposed to dissociate on the hot ground electronic state via collision-induced internal conversion. A two-body dissociation channel is favored leading to HCl and CH2CO, followed by secondary dissociation. © 2010 American Chemical Society.
Tsai, P-Y, Lin K-C.  2015.  Insight into photofragment vector correlation by a multi-center impulsive model. Physical Chemistry Chemical Physics. 17:19592-19601., Number 29 AbstractWebsite

A multi-center impulsive model has been recently developed to characterize the dynamic feature of product energy distribution in photodissociation of formaldehyde, H2CO → CO + H2. (J. Phys. Chem. A, 2015, 119, 29) The model is extended to predict the vector correlations among transition dipole moment μ of the parent molecule, recoil velocity v and rotational angular momentum j of the fragments produced via the transition state (TS) and roaming path. The correlation results of μ-j, j-j and μ-v vectors of the fragments are consistent with those reported using quasi-classical trajectory simulation on the global potential energy surface. In contrast to the TS route, the vector properties via the roaming path are loosely correlated. This work offers an alternative method to study stereodynamics of the photodissociation process, and is conducive to clarifying the origin of photofragment vector correlation especially for the roaming pathway. This journal is © the Owner Societies.
Hu, E-L, Tsai P-Y, Fan H, Lin K-C.  2013.  Photodissociation of gaseous CH3COSH at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Observation of three dissociation channels. Journal of Chemical Physics. 138, Number 1 AbstractWebsite

Upon one-photon excitation at 248 nm, gaseous CH3C(O)SH is dissociated following three pathways with the products of (1) OCS + CH 4, (2) CH3SH + CO, and (3) CH2CO + H 2S that are detected using time-resolved Fourier-transform infrared emission spectroscopy. The excited state 1(nO, π *CO) has a radiative lifetime of 249 ± 11 ns long enough to allow for Ar collisions that induce internal conversion and enhance the fragment yields. The rate constant of collision-induced internal conversion is estimated to be 1.1 × 10-10 cm3 molecule -1 s-1. Among the primary dissociation products, a fraction of the CH2CO moiety may undergo further decomposition to CH2 + CO, of which CH2 is confirmed by reaction with O2 producing CO2, CO, OH, and H2CO. Such a secondary decomposition was not observed previously in the Ar matrix-isolated experiments. The high-resolution spectra of CO are analyzed to determine the ro-vibrational energy deposition of 8.7 ± 0.7 kcal/mol, while the remaining primary products with smaller rotational constants are recognized but cannot be spectrally resolved. The CO fragment detected is mainly ascribed to the primary production. A prior distribution method is applied to predict the vibrational distribution of CO that is consistent with the experimental findings. © 2013 American Institute of Physics.
Nakamura, M, Palazzetti F, Tsai P-Y, Lin K-C, Kasai T, Che D-C, Lombardi A, Aquilanti V.  2019.  Vectorial imaging of the photodissociation of 2-bromobutane oriented: Via hexapolar state selection. Physical Chemistry Chemical Physics. 21(26):14164-14172. AbstractWebsite

Molecular orientation techniques are becoming available in the study of elementary chemical processes, in order to highlight those structural and dynamical properties that would be concealed by random rotational motions. Recently successful orientation was achieved for asymmetric-top and chiral molecules of much larger complexity than hitherto. In this work, we report and discuss the correlation between the vectors' photofragment recoil velocity v, transition dipole moment μ, and permanent dipole moment d in a dissociation experiment on hexapole oriented 2-bromobutane, photoinitiated by a linearly polarized laser. The sliced ion images of the Br∗(2P1/2) and Br(2P3/2) photofragments were acquired at 234.0 and 254.1 nm, respectively, by a (2 + 1) resonance-enhanced multiphoton ionization technique. A detailed analysis of the sliced ion images obtained at a tilting angle 45° of laser polarization provides information on the correlation of the three vectors, which are confined by two polar angles α and χ and one azimuthal angle φμd in the recoil frame. The sliced ion images of Br fragments eliminated individually from the enantiomers at 254.1 nm yield an asymmetric factor close to zero; for this reason the photofragment angular distributions do not show significant differences. The elimination of the Br∗ fragment at 234.0 nm is mainly correlated with a parallel transition, giving rise to a large anisotropy parameter of 1.85, and thus can be considered as a single state excitation. The resulting recoil frame angles are optimized to 163° ± 8° and 164° ± 1° for α and χ, respectively, whereas φμd is approaching 0° for the best fit. Since for the present molecule, the three vectors have an only slight spatial arrangement, the photofragment angular distributions of the two enantiomers do not show appreciable differences. Theoretical and computational simulations provide us the basis to state that oriented enantiomers can be discriminated on-the-fly in photodissociation processes even initiated by non-circularly polarized light, provided that the three vectors encountered above have specific three-dimensional arrangements. The fact that Br fragment elimination involves a multi-potential dissociation carries uncertainties in theoretical estimates of the vector direction. Therefore, this work represents a preliminary but significant step on the road to chiral discrimination on-the-fly, which is shown to be best propitiated in molecules where vectors are far from having degenerate mutual angular directions. © 2019 the Owner Societies.
Li, H-K, Tsai P-Y, Hung K-C, Kasai T, Lin K-C.  2015.  Communication: Photodissociation of CH3CHO at 308 nm: Observation of H-roaming, CH3-roaming, and transition state pathways together along the ground state surface. Journal of Chemical Physics. 142, Number 4 AbstractWebsite

Following photodissociation of acetaldehyde (CH3CHO) at 308 nm, the CO(v = 1-4) fragment is acquired using time-resolved Fourier-transform infrared emission spectroscopy. The CO(v = 1) rotational distribution shows a bimodal feature; the low- and high-J components result from H-roaming around CH3CO core and CH3-roaming around CHO radical, respectively, in consistency with a recent assignment by Kable and co-workers (Lee et al., Chem. Sci. 5, 4633 (2014)). The H-roaming pathway disappears at the CO(v 2) states, because of insufficient available energy following bond-breaking of H + CH3CO. By analyzing the CH4 emission spectrum, we obtained a bimodal vibrational distribution; the low-energy component is ascribed to the transition state (TS) pathway, consistent with prediction by quasiclassical trajectory calculations, while the high-energy component results from H- and CH3-roamings. A branching fraction of H-roaming/CH3-roaming/TS contribution is evaluated to be (8% ± 3%)/(68% ± 10%)/(25% ± 5%), in which the TS pathway was observed for the first time. The three pathways proceed concomitantly along the electronic ground state surface. © 2015 AIP Publishing LLC.
Kao, M-J, Chen C-H, Tsai P-Y, Lim T-S, Lin K-C, Luh T-Y.  2011.  Hydrogen-bonding-induced one-handed helical polynorbornenes appended with chiral alaninegland. Macromolecular Chemistry and Physics. 212:2328-2338., Number 21 AbstractWebsite

Polynorbornenes appended with anthracene and chiral alanine linkers are synthesized. Hydrogen bonding between the adjacent bisamidic linkers brings adjacent anthracene chromophores in a more suitable orientation for exciton coupling and renders one-handed helical structures for these polymers. Excimer formation is observed from their emission spectra. Monoamidic linkers provide only one hydrogen bond, which would be less robust and result in much lower circular dichroic response. Hydrogen bonding between the adjacent chiral alanine linkers brings appended anthracene in a more suitable orientation for exciton coupling and excimer formation, rendering one-handed helical structures in polynorbornenes. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Lin, K-C, Tsai P-Y, Chao M-H, Nakamura M, Kasai T, Lombardi A, Palazzetti F, Aquilanti V.  2018.  Roaming signature in photodissociation of carbonyl compounds. International Reviews in Physical Chemistry. 37:217-258., Number 2 AbstractWebsite

An alternative to the transition state (TS) pathway, the roaming route, which bypasses the minimum energy path but produces the same molecular products, was recently found in photodissociation dynamics. This account describes signatures of roaming in photodissociation of the carbonyl compounds, specifically methyl formate and aliphatic aldehydes. Methyl formate was promoted to the excited state, followed by internal conversion via a conical intersection. Then, the energetic precursor dissociated to fragments which proceeded along either TS or roaming path. In contrast to the lack of a roaming saddle point found in methyl formate, the structure of the roaming saddle point for each of a series of aliphatic aldehydes comprises two moieties that are weakly bound at a distance. As its size increases, the energy difference between the TS barrier and the roaming saddle point increases and the roaming pathway becomes increasingly dominant. Experimentally, the rotational-level dependence of the roaming route was measured with ion imaging, while the vibrational-state dependence was observed with time-resolved Fourier-transform infrared emission spectroscopy. The roaming signature was verified theoretically by quasi-classical trajectory (QCT) calculations. As an alternative to the QCT method, a multi-center impulsive model was developed to simulate the roaming scalar and vector properties. © 2018 Informa UK Limited, trading as Taylor & Francis Group.
Lin, K-C, Hung K-C, Tsai P-Y, Li H-K.  2014.  Photodissociation of CH3CHO at 248 nm by time-resolved Fourier-transform infrared emission spectroscopy: Verification of roaming and triple fragmentation. Journal of Chemical Physics. 140, Number 6 AbstractWebsite

By using time-resolved Fourier-transform infrared emission spectroscopy, the HCO fragment dissociated from acetaldehyde (CH3CHO) at 248 nm is found to partially decompose to H and CO. The fragment yields are enhanced by the Ar addition that facilitates the collision-induced internal conversion. The channels to CH2CO + H2 and CH3CO + H are not detected significantly. The rotational population distribution of CO, after removing the Ar collision effect, shows a bimodal feature comprising both low- and high-rotational (J) components, sharing a fraction of 19% and 81%, respectively, for the vibrational state v = 1. The low-J component is ascribed to both roaming pathway and triple fragmentation. They are determined to have a branching ratio of <0.13 and >0.06, respectively, relative to the whole v = 1 population. The CO roaming is accompanied by a highly vibrational population of CH4 that yields a vibrational bimodality. © 2014 AIP Publishing LLC.
Chen, S-Y, Tsai P-Y, Lin H-C, Wu C-C, Lin K-C, Sun BJ, Chang AHH.  2011.  I2 molecular elimination in single-photon dissociation of CH2I2 at 248 nm by using cavity ring-down absorption spectroscopy. Journal of Chemical Physics. 134, Number 3 AbstractWebsite

Following single-photon dissociation of CH2I2 at 248 nm, I2 molecular elimination is detected by using cavity ring-down absorption spectroscopy. The technique comprises two laser beams propagating in a perpendicular configuration, in which a tunable laser beam along the axis of the ring-down cell probes the I2 fragment in the B 3 ou + - X 1 g + transition. The nascent vibrational populations for v 0, 1, and 2 levels are obtained with a population ratio of 1:(0.65 0.10):(0.30 0.05), corresponding to a Boltzmann-like vibrational temperature of 544 73 K. The quantum yield of the ground state I2 elimination reaction is determined to be 0.0040 0.0025. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state CH2I2 via internal conversion, followed by asynchronous three-center dissociation. A positive temperature effect supports the proposed mechanism. © 2011 American Institute of Physics.
Chang, Y-P, Tsai P-Y, Lee H-L, Lin K-C.  2013.  Interfacial electron transfer from CdSe/ZnS quantum dots to TiO2 nanoparticles: Linker dependence at single molecule level. Electroanalysis. 25:1064-1073., Number 4 AbstractWebsite

We utilize single molecule spectroscopy combined with time-correlated single-photon counting to probe electron transfer (ET) kinetics from CdSe/ZnS (core/shell) quantum dots (QDs) to TiO2 through various lengths of linker molecules. The QD-linker-TiO2 complexes with varied linker length, linker structure, and QD size are fabricated by a surface-based stepwise method to show control of the rate and of the magnitude of fluctuations of photo-induced ET at the single molecule level. The ET rate constants are determined to be 2.8×107, 1.9×107, and 3.5×106s-1 for the chain length of 1.5, 6.2 and 13.8Å, respectively. The electronic coupling strengths between QDs and TiO2 are further calculated to be 3.68, 3.60, and 1.59cm-1 for the three different chain lengths by using the Marcus ET model. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Tsai, P-Y, Lin K-C.  2010.  Fine structure-resolved rotational energy transfer of SH (A 2Σ+, v′ = 0) state by collisions with Ar. Physical Chemistry Chemical Physics. 12:1162-1171., Number 5 AbstractWebsite

Rotational energy transfer (RET) by Ar collisions within the v′ = 0 level of the SH A2Σ+ state is probed using a laser-induced dispersed fluorescence technique, following photodissociation of H2S at 248 nm. The Ar pressure is adjusted appropriately to allow for significant observation of the single-collision induced RET process. The spin-resolved and spin-averaged rate constants are then evaluated with the aid of a kinetic model under single-collision conditions. The theoretical counterparts are calculated using a quantum scattering method, in which a newly fitted potential energy function is based on ab initio potential energy surface reported previously. The experimental and theoretical kinetic data are essentially consistent in the trend of N and ΔN dependence. Several propensity rules are found in the RET collisions. For instance, for ΔN = 1, 2, and 3, the rate constants decrease with increasing N or ΔN. Given a fixed ΔN, the rate constants of the same initial N in the downward transition appear to be larger than those in the upward transitions. In ΔN = 0, the F2 → F1 transitions prevail over the F 1 → F2 transitions (F1 = N + 1/2, F 2 = N - 1/2), whereas in ΔN ≠ 0, the fine-structure- conserving collisions are more favored than the fine-structure-changing collisions. The principle of microscopic reversibility is also examined for both experimental and theoretical kinetic data, showing that translational energies of the RET collisions are close to thermal equilibrium at room temperature. The propensity rules may be rationalized according to this principle. © 2010 the Owner Societies.
Tsai, P-Y, Lin K-C.  2015.  Insight into the photodissociation dynamical feature of conventional transition state and roaming pathways by an impulsive model. Journal of Physical Chemistry A. 119:29-38., Number 1 AbstractWebsite

Without the need to construct complicated potential energy surfaces, a multicenter impulsive model is developed to characterize the dynamical feature of conventional transition state (TS) and roaming pathways in the photodissociation of formaldehyde, H2CO → CO + H2. The photofragment energy distributions (PED) resulting from the roaming mechanism are found to closely correlate to a particular configuration that lies close to the edge of the plateau-like intrinsic reaction coordinate, whereas such a PED is associated with the configuration at the saddle point when the conventional TS pathway is followed. The evaluated PED results are consistent with those by experimental findings and quasi-classical trajectory calculations. Following impulsive analysis, the roaming pathway can be viewed as a consequence of energy transfer events between several vibrational modes. For H2CO, the available energy initially accumulated at the C-H bond is transferred to other transitional mode(s) via stretching-bending coupling, and finally to the HH stretching. (Chemical Presented). © 2014 American Chemical Society.
Tsai, P-Y, Lin K-C.  2012.  Rotational energy transfer of SH(X 2 Π, v′=0, J′=0.5-10.5) by collision with Ar: λ-doublet resolved transition propensity. ChemPhysChem. 13:274-280., Number 1 AbstractWebsite

The behavior of λ-doublet resolved rotational energy transfer (RET) by Ar collisions within the SH(X 2Π, v′=0) state is characterized. The matrix elements of terms in the interaction potential responsible for interference effects are calculated to explain the propensity rules for collision-induced transitions within and between spin-orbit manifolds. In this manner, the physical mechanisms responsible for the F 1-F 1, F 2-F 2, and F 1-F 2 transitions may be reasonably identified. As collision energy increases, the propensity for collisional population of the final e or f level is replaced by the e/f-conserving propensity. Such a change in propensity rule can be predicted in terms of energy sudden approximation at high J limit for the pure Hund's case scheme. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.