Subject Area物理化学
Photodissociation of Methanol at 157nm
Chen ZC(陈志超); Zhang YW(张永为); Liu FC(刘福春); Jiang B(姜波); 戴维.派克; Yang XM(杨学明)
Conference NameXXIII International Symposium on Molecular Beams
Conference Date2009-6-1
Conference Place中国
Funding Organization中国科学院大连化学物理研究所
AbstractThe photochemistry of methanol, CH3OH, is of practical importance in atmospheric chemistry, and it presents an interesting set of fundamental questions regarding vibrational mode selectivity, and sequential versus concerted bond breaking1-6. CH3OH provides all the complexities of large polyatomic molecule photodissociation while yielding simple product fragments that are efficiently detected using laser ionization. We investigated the photodissociation of methanol following VUV absorption at 157nm using velocity map imaging7 of CH3(v000) via the 3p (333.5nm) Rydberg states to map out the information of the dissociation channel. The images shown below reveal two kinds of methyl radical products: ‘fast’ and ‘slow’ CH3. ‘Fast’ CH3 arises from direct dissociation of CH3OH + hvdis  CH3 + OH (1), in which the initially excited 21A’’ state of CH3OH directly dissociates. A vibrational-resolved kinetic energy release spectra can be abstracted from this part of the image, for the first time! The OH vibrationally state is inverted and peaks at v=4, and exhibits a highly anisotropic angular distribution with β ~ -0.70. The ‘slow’ CH3 arises from a two-step process: CH3OH + hvdiss  CH3O + H (2), then CH3O + hvdet  CH3 + O (3). After the first step dissociation (2), there is very broad internal energy distribution for the CH3O fragments, from 0 kcal/mol to 60 kcal/mol. The unstructured ‘slow’ CH3 reveals the dissociation of CH3O by absorption of one detection laser photon (333.5nm). The photodissociation of CH3O with low internal energy limit is via the CH3O ground state and the relative product is O(3PJ), while photodissociation of CH3O with high internal energy is via the A state, and the relative product is O(1D2). Between the ‘fast’ and ‘slow’ CH3 signals, there is a rather broad peak. It is too broad to assign it to the direct dissociation process (1). However, there is a large gap between the two-step photodissociation area and this peak. Because of the crossing of potential energy curves, predissociation of CH3O happens around the energy area corresponding to this peak. It appears that the peak in question arises from two-step photodissociation via predissociation, where CH3O predissociates via the A state, and the relative product is O(3PJ).
Document Type会议论文
Corresponding AuthorYang XM(杨学明)
Recommended Citation
GB/T 7714
Chen ZC,Zhang YW,Liu FC,et al. Photodissociation of Methanol at 157nm[C],2009:99/2.
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