Flash Photolysis of Polystyrene with Laser
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Flash Photolysis of Polystyrene with Laser Ma Hongwei Tang Yongjian Cui Baoshun Institute of Nuclear Physics and Chemistry, CAEP, P.O.Box 919-987, 621900, Mianyang, China Gao wende Liu Weiming Wang Shouwen Ma Hong Ao Shiqing Deng Wanhui Xu Jianguang Chemistry Department, Sichuan University, Chengdu, China, 610064 Abstract This paper describes the photolysis of polystyrene with 1.06µm laser. The laser dissociation is measured with mass spectrum method. It gives the mean mass value of particles, quantum value and percentage of m/e=104 vs time. Introduction The study of organic compound with infrared laser is focused in the infrared region. Using the special vibration film of polyatomic molecule that has resonant, near resonant and multiple photon absorption to laser of given wavelength, or using other indirect exciting method, chemical reaction can be excited in the molecule. In infrared band, photon energy is between the energy needed by base frequency vibration and that needed by electron state excitation. Even though most of the molecules have absorption, the absorption cross-section is very small. Therefore, little chemistry study with laser has been done at that band, and even less study has been done on polymer compound. In this paper, photolysis of polymer compound under high power density laser irradiation is presented in attempt to put forward some inspiration about the flash stability and related chemical behavior. Experiment and the result The wavelength, output energy and pulse width of the pulsed Nd-glass laser used in the experiment are respectively 1.06µm, 2.5J and at the order of 10−4s. In Q-switched operation, the pulse width is at the order of 10−8s and the output energy is 0.5J. Finnigan MAT4510 chromatograph/mass spectrometer was used for the fragment analysis in time. The experiment device is shown in figure 1. 1.06µm laser is focused with a lens. The focal length is 15cm. And the laser spot diameter is 0.5mm. The focused laser beam passes through the window in the ion source of the mass spectrometer and irradiates at the center of the ion volume. The vacuum of the ion source is 13µPa. Since 1.06µm laser is difficult to adjust because it is invisible infrared light, a He-Ne laser is used as an auxiliary light source, which is coaxial with Nd: phosphate glass laser used in our laboratory. When the red He-Ne laser spot is located on the sample, the 1.06µm infrared laser spot is also located there [1~4]. The molecule weight of the polystyrene sample is 2.68×105. The ion volume is a cylinder made up of stainless steel pipe with S5.7.1
thin wall. A small hole of 1mm in diameter is drilled in the right side of the cylinder. Polystyrene sample is put on the inner wall of the ion volume to face the hole. The polystyrene sample melts at 180°C (polystyrene melts at 150°C~180°C and decomposes at 300°C) and adheres to the inner wall of the ion volume. Then, the sample is put into the ion source with a bar. The focused pulsed laser beam irradiates the sample through the small hole in the ion volume to decomp
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