Browsing by Author "Chiang, Hung-Chu"

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Distribution of Vibrational States of CO(2) in the Reaction O((1)D) + CO(2) from Time-Resolved Fourier Transform Infrared Emission Spectra
(2009-04-16)
Chen, Hui-Fen
;
Chiang, Hung-Chu
;
Matsui, Hiroyuki
;
Tsuchiya, Soji
;
Lee, Yuan-Pern
A mixture Of O(3) and CO(2) was irradiated with light from a KrF laser at 248 nm; time-resolved infrared emission Of CO(2) in the region 2000-2400 cm(-1) was observed with a Fourier transform spectrometer. This emission involves one quantum in the asymmetric stretching mode (nu(3)) Of CO(2) in highly vibrationally excited states. The band contour agrees satisfactorily with a band shape calculated based on a simplified polyad model of CO(2) and a vibrational distribution estimated through a statistical partitioning of energy of similar to 13 000 cm(-1), similar to 3100 cm(-1) smaller than the available energy, into the vibrational modes Of CO(2). From this model, approximately 44% and 5% of the available energy of O((1)D) + CO(2) is converted into the vibrational and rotational energy of product CO(2), respectively, consistent with previous reports of similar to 50% for the translational energy. An extent of rotational excitation Of CO(2) much smaller than that expected from statistical calculations indicates a mechanism that causes a small torque to be given to CO(2) when an O atom leaves the complex CO(3) on the triplet exit surface of potential energy, consistent with quantum-chemical calculations.
Distribution of Vibrational States of CO2 in the Reaction O(D-1) + CO2 from Time-Resolved Fourier Transform Infrared Emission Spectra
(2009-04-16)
Chen, Hui-Fen
;
Chiang, Hung-Chu
;
Matsui, Hiroyuki
;
Tsuchiya, Soji
;
Lee, Yuan-Pern
A mixture Of O-3 and CO2 was irradiated with light from a KrF laser at 248 nm; time-resolved infrared emission Of CO2 in the region 2000-2400 cm(-1) was observed with a Fourier transform spectrometer. This emission involves one quantum in the asymmetric stretching mode (nu(3)) Of CO2 in highly vibrationally excited states. The band contour agrees satisfactorily with a band shape calculated based on a simplified polyad model of CO2 and a vibrational distribution estimated through a statistical partitioning of energy of similar to 13 000 cm(-1), similar to 3100 cm(-1) smaller than the available energy, into the vibrational modes Of CO2. From this model, approximately 44% and 5% of the available energy of O(D-1) + CO2 is converted into the vibrational and rotational energy of product CO2, respectively, consistent with previous reports of similar to 50% for the translational energy. An extent of rotational excitation Of CO2 much smaller than that expected from statistical calculations indicates a mechanism that causes a small torque to be given to CO2 when an O atom leaves the complex CO3 on the triplet exit surface of potential energy, consistent with quantum-chemical calculations.
Electroabsorption spectra of push-pull porphyrins in solution and in solid films
(2015-01-01)
Awasthi, Kamlesh
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Hsu, Hung-Yu
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Chiang, Hung-Chu
;
Mai, Chi-Lun
;
Yeh, Chen-Yu
Polarized electroabsorption (E-A) spectra of highly efficient porphyrin sensitizers (YD2 and YD2-oC8) have been measured in benzene solution. Polarized E-A spectra of these push-pull porphyrins embedded in poly(methyl methacrylate) films or sensitized on TiO2 films are also observed. Based on the analysis of the E-A spectra, the magnitude of the electric dipole moment both in the ground state and in the lowest excited state have been evaluated in solution and in solid films. The electric dipole moment in the excited state of these compounds is very large on TiO2 films, suggesting the interfacial charge transfer on TiO2 surface following photoexcitation of porphyrin dyes. The electric dipole moment in the excited state evaluated from the E-A spectra is very different from the one evaluated from the electrophotoluminescence spectra on TiO2, suggesting that the strong local field of TiO2 films is applied to the fluorescing dyes attached to TiO2 films.
Field-Induced Fluorescence Quenching and Enhancement of Porphyrin Sensitizers on TiO2 Films and in PMMA Films
(2013-11-28)
Hsu, Hung-Yu
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Chiang, Hung-Chu
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Hu, Jyun-Yu
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Awasthi, Kamlesh
;
Mai, Chi-Lun
Three highly efficient porphyrin sensitizers-YD2, YD2-oC8, and YD30, either sensitized on TiO2 films or embedded in PMMA films were investigated using electrophotoluminescence (E-PL) spectra. Under both thin-film conditions, on application of an external electric field we observed the quenching of fluorescence of push-pull porphyrins (YD2 and YD2-oC8) and a slightly enhanced fluorescence of the reference porphyrin without an electron donor group (YD30). A nonfluorescent state with charge separation (CS) is proposed to be involved in both YD2 and YD2-oC8 systems so that the electron injection becomes accelerated in the presence of a strong electric field. In contrast, the retardation of the nonradiative process not involving a CS state was the reason for the field-induced enhancement of fluorescence of YD30. The extent of fluorescence quenching of YD2-oC8 was greater than that of YD2 on TiO2 films, indicating that the ortho-substituted long alkoxyl chains play a key role to accelerate the consecutive electron injection involving the CS state. Our E-PL results indicate that a field-induced variation of fluorescent intensity is related to the efficiency of conversion of solar energy and that further improvement of the performance of devices containing push pull porphyrin dyes is achievable under an applied electric field.
Reaction Dynamics of O((1)D,(3)P) + OCS Studied with Time-Resolved Fourier Transform Infrared Spectroscopy and Quantum Chemical Calculations
(2009-11-26)
Chiang, Hung-Chu
;
Wang, Niann-Shiah
;
Tsuchiya, Soji
;
Chen, Hsin-Tsung
;
Lee, Yuan-Pern
Time-resolved infrared emission of CO(2) and OCS was observed in reactions O((1)P) + OCS and O((1)D) + OCS with a step-scan Fourier transform spectrometer. The CO(2) emission involves Delta nu(3) = -1 transitions from highly vibrationally excited states, whereas emission of OCS is mainly from the transition (0, 0 degrees, 1) (0, 0, 0); the latter derives its energy via near-resonant V-V energy transfer from highly excited CO(2). Rotationally resolved emission lines of CO (v <= 4 and J <= 30) were also observed in the reaction O((1)D) + OCS. For O((3)P) + OCS, weak emission Of CO(2) diminishes when Ar is added, indicating that O((3)P) is translationally hot to overcome the barrier for CO(2) formation. The band contour of CO(2) agrees with a band shape simulated on the basis of a Dunharn expansion model of CO(2); the average vibrational energy of CO(2) in this channel is 49% of the available energy. This vibrational distribution fits with that estimated through a statistical partitioning of energy E* congruent to 18 000 +/- 500 cm(-1) into all vibrational modes of CO(2). For the reaction of O((1)D) + OCS, approximately 51% of the available energy is converted into vibrational energy of CO(2), and a statistical prediction using E* congruent to 30 000 +/- 500 cm(-1) best fits the data. The mechanisms of these reactions are also investigated with the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) method. The results indicate that the triplet O((3)P) + OCS(X(1)Sigma(+)) surface proceeds via direct abstraction and substitution channels with barriers of 27.6 and 36.4 kJ mol(-1), respectively, to produce SO(X(3)Sigma(-)) + CO(X(1)Sigma(+)) and S((3)P) + CO(2)(X(1)A(1)), whereas two intermediates, OSCO and SC(O)O, are formed from the singlet O((1)D) + OCS(X(1)Sigma(+)) surface without barrier, followed by decomposition to SO(a(1)Delta) + CO(X(1)Sigma(+)) and S((1)D) + CO(2)(X(1)A(1)), respectively. For the ground-state reaction O((3)P) + OCS(X(1)Sigma(+)), the singlet-triplet curve crossings play important roles in the observed kinetics and chemiluminescence.
Reaction Dynamics of O(D-1,P-3) + OCS Studied with Time-Resolved Fourier Transform Infrared Spectroscopy and Quantum Chemical Calculations
(2009-11-26)
Chiang, Hung-Chu
;
Wang, Niann-Shiah
;
Tsuchiya, Soji
;
Chen, Hsin-Tsung
;
Lee, Yuan-Pern
Time-resolved infrared emission of CO2 and OCS was observed in reactions O(P-1) + OCS and O(D-1) + OCS with a step-scan Fourier transform spectrometer. The CO2 emission involves Delta nu(3) = -1 transitions from highly vibrationally excited states, whereas emission of OCS is mainly from the transition (0, 0 degrees, 1) (0, 0, 0); the latter derives its energy via near-resonant V-V energy transfer from highly excited CO2. Rotationally resolved emission lines of CO (v <= 4 and J <= 30) were also observed in the reaction O(D-1) + OCS. For O(P-3) + OCS, weak emission Of CO2 diminishes when Ar is added, indicating that O(P-3) is translationally hot to overcome the barrier for CO2 formation. The band contour of CO2 agrees with a band shape simulated on the basis of a Dunharn expansion model of CO2; the average vibrational energy of CO2 in this channel is 49% of the available energy. This vibrational distribution fits with that estimated through a statistical partitioning of energy E* congruent to 18 000 +/- 500 cm(-1) into all vibrational modes of CO2. For the reaction of O(D-1) + OCS, approximately 51% of the available energy is converted into vibrational energy of CO2, and a statistical prediction using E* congruent to 30 000 +/- 500 cm(-1) best fits the data. The mechanisms of these reactions are also investigated with the CCSD(T)/6-311+G(3df)//B3LYP/6-311+G(3df) method. The results indicate that the triplet O(P-3) + OCS(X-1 Sigma(+)) surface proceeds via direct abstraction and substitution channels with barriers of 27.6 and 36.4 kJ mol(-1), respectively, to produce SO(X-3 Sigma(-)) + CO(X-1 Sigma(+)) and S(P-3) + CO2(X(1)A(1)), whereas two intermediates, OSCO and SC(O)O, are formed from the singlet O(D-1) + OCS(X-1 Sigma(+)) surface without barrier, followed by decomposition to SO(a(1)Delta) + CO(X-1 Sigma(+)) and S(D-1) + CO2(X(1)A(1)), respectively. For the ground-state reaction O(P-3) + OCS(X-1 Sigma(+)), the singlet-triplet curve crossings play important roles in the observed kinetics and chemiluminescence.