Photodissociation of OCS, SH/SD and O2 and atomic polarization. By development and application of velocity map imaging
Nijmegen : [S.n.]
Number of pages
RU, Molecular and Laser Physics, 23 april 2007
Promotores : Parker, D.H., Yang, X.
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Molecular and Laser Physics
SubjectMolecular and Laser Physics
The scope of this thesis is twofold: one, development and applications of the velocity map imaging (VMI) technique; the other, investigation of atomic polarization arising from the photodissociation of small molecules. A general introduction is given in chapter 1, and the rest is divided into: Part I (chapters 2-4), Part II (chapters 5-9), and Appendices. Part I, experimental development and applications, starts with evaluating the VMI experiment. The analysis provides essential knowledge for the key elements that an 'imager' pursues. Several useful accessories, namely photoion time-of-flight (TOF) mass spectrometry, resonance-enhanced-multiphoton-ionization (REMPI) spectroscopy, and applications of SMI, are demonstrated. 'Doppler slicing', 'optical slicing', 'time slicing' and 'Doppler-free imaging' are studied. A uniform optical slicing and a good crush condition using time-lag focusing are used for the first time. A 3D image is also demonstrated.Part II, atomic polarization following the photodissociation of OCS, SH/SD and O2, starts by introducing product atomic polarization and related photodissociation dynamics. Unexpected structured S+ signals were observed in the photoexcitation of carbonyl sulfide (OCS) at 157 nm. The S+ signals have been shown to arise from the photodissociation of OCS followed by photoionization of S(1S0). Completely polarized S(1D2) from the photodissociation of SH/SD(high v) has been observed at 288 and 291 nm. Atomic S(1D2) photofragment is produced via the A 2(Sigma)+ state. The S(1D2) product is aligned, in which the total angular momentum J is perpendicular to the recoil velocity v. The experimental results are well predicted by the diabatic model. A thorough study of the photodissociation of O2 via the B 3(Sigma)u-state is presented. The study shows that the angular momentum J of the O(1D2) product is aligned predominantly perpendicular to the recoil velocity v. Similar to the SH study, the diabatic model describes the O(1D2) alignment fairly well, but poorly describes the O(3PJ) fine-structure branching ratios. Preliminary results of the O(3P) + O(3P) channel and several accompanying REMPI photoelectron images have also been presented. Finally, the precessional motion of the O(1D2) photo-products in an applied magnetic field has been visualized, by means of the 'movies'. This also provides an alternative method to study atomic polarization arising from photodissociation. In the appendices, problems leading to 'imperfect' images, and a correction procedure is demonstrated. Several fascinating 'movies' are embedded in this thesis.
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