King-Chuen Lin
National Taiwan University, Taiwan
Title: Some Applications of Laser-based Ionization Mass Spectrometer in Molecular Photodissociation
Biography
Biography: King-Chuen Lin
Abstract
By using the time-of-flight mass spectrometer, we have provided insight into interrelation of the ionization and fragmentation mechanism of ketene. When a resonance-enhanced multiphoton ionization (REMPI) technique is applied via the Rydberg state, the (2+1) REMPI process leads to a direct photoionization of ketene under a low ionizing laser energy. When the (2+2) REMPI process dominates, the ketene ion is produced by the rovibrational autoionization of a super excited state.
The second application is to investigate competitive bond dissociation mechanisms for bromoacetyl chloride, 2- and 3-bromopropionyl chlorides following the transition 1 [n(O)®π* (C=O)] at 234-235 nm. The branching ratios of C-Br/C-Cl bond fission were evaluated to be 0.47, 0.24, and 0.098, respectively, by using (2+1) REMPI technique equipped with velocity ion imaging. The mechanisms for C-Cl and C-Br bond fission are discussed.
If time is allowed, we will report photodissociation dynamics of methyl formate HCOOCH3 at photolysis wavelengths from 225 to 255 nm. Ion imaging of CO and H are acquired. The translational energy distributions of CO comprise three channels of triple fragmentation, roaming and transition state (TS) processes, as photolysis wavelength is <248 nm. In contrast, the CO distribution is contributed by the roaming and the TS processes at >248 nm