Browsing by Author "Lin, Ming-Fu"

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Photodissociation dynamics of nitrobenzene and o-nitrotoluene
(2007-02-14)
Lin, Ming-Fu
;
Lee, Yuan T.
;
Ni, Chi-Kung
;
Xu, Shucheng
;
Lin, M. C.
Photodissociation of nitrobenzene at 193, 248, and 266 nm and o-nitrotoluene at 193 and 248 nm was investigated separately using multimass ion imaging techniques. Fragments corresponding to NO and NO2 elimination from both nitrobenzene and o-nitrotoluene were observed. The translational energy distributions for the NO elimination channel show bimodal distributions, indicating two dissociation mechanisms involved in the dissociation process. The branching ratios between NO and NO2 elimination channels were determined to be NO/NO2=0.32 +/- 0.12 (193 nm), 0.26 +/- 0.12 (248 nm), and 0.4 +/- 0.12(266 nm) for nitrobenzene and 0.42 +/- 0.12(193 nm) and 0.3 +/- 0.12 (248 nm) for o-nitrotoluene. Additional dissociation channels, O atom elimination from nitrobenzene, and OH elimination from o-nitrotoluene, were observed. New dissociation mechanisms were proposed, and the results are compared with potential energy surfaces obtained from ab initio calculations. Observed absorption bands of photodissociation are assigned by the assistance of the ab initio calculations for the relative energies of the triplet excited states and the vertical excitation energies of the singlet and triplet excited states of nitrobenzene and o-nitrotoluene. Finally, the dissociation rates and lifetimes of photodissociation of nitrobenzene and o-nitrotoluene were predicted and compared to experimental results. (c) 2007 American Institute of Physics.
Photodissociation dynamics of nitrobenzene and o-nitrotoluene
(2007-02-14)
Lin, Ming-Fu
;
Lee, Yuan T.
;
Ni, Chi-Kung
;
Xu, Shucheng
;
Lin, M. C.
Photodissociation of nitrobenzene at 193, 248, and 266 nm and o-nitrotoluene at 193 and 248 nm was investigated separately using multimass ion imaging techniques. Fragments corresponding to NO and NO2 elimination from both nitrobenzene and o-nitrotoluene were observed. The translational energy distributions for the NO elimination channel show bimodal distributions, indicating two dissociation mechanisms involved in the dissociation process. The branching ratios between NO and NO2 elimination channels were determined to be NO/NO2=0.32 +/- 0.12 (193 nm), 0.26 +/- 0.12 (248 nm), and 0.4 +/- 0.12(266 nm) for nitrobenzene and 0.42 +/- 0.12(193 nm) and 0.3 +/- 0.12 (248 nm) for o-nitrotoluene. Additional dissociation channels, O atom elimination from nitrobenzene, and OH elimination from o-nitrotoluene, were observed. New dissociation mechanisms were proposed, and the results are compared with potential energy surfaces obtained from ab initio calculations. Observed absorption bands of photodissociation are assigned by the assistance of the ab initio calculations for the relative energies of the triplet excited states and the vertical excitation energies of the singlet and triplet excited states of nitrobenzene and o-nitrotoluene. Finally, the dissociation rates and lifetimes of photodissociation of nitrobenzene and o-nitrotoluene were predicted and compared to experimental results. (c) 2007 American Institute of Physics.
Photodissociation dynamics of phenol
(2007-09-27)
Tseng, Chien-Ming
;
Lee, Yuan T.
;
Lin, Ming-Fu
;
Ni, Chi-Kung
;
Liu, Suet-Yi
The photodissociation of phenol at 193 and 248 nm was studied using multimass ion-imaging techniques and step-scan time-resolved Fourier-transform spectroscopy. The major dissociation channels at 193 nm include cleavage of the OH bond, elimination of CO, and elimination of H2O. Only the former two channels are observed at 248 nm. The translational energy distribution shows that H-atom elimination occurs in both the electronically excited and ground states, but elimination of CO or HO occurs in the electronic ground state. Rotationally resolved emission spectra of CO (1 <= v <= 4) in the spectral region of 1860-2330 cm(-1) were detected upon photolysis at 193 nm. After a correction for rotational quenching, CO (v 4) shows a nascent rotational temperature of similar to 4600 K. The observed vibrational distribution of (v = 1)1(v 2)/(v = 3)/(v = 4) = 64.3/22.2/9.1/4.4 corresponds to a vibrational temperature of 3350 +/- 20 K. An average rotational energy of 6.9 +/- 0.7 kcal mol(-1) and vibrational energy of 3.8 +/- 0.7 kcal mol(-1) are observed for the CO product. The dissociation channels, translational energy distributions of the photofragment, and vibrational and rotational energies of product CO are consistent with potential energy surfaces from quantum chemical calculations and the branching ratios from an RRKM calculation.