本研究於室溫下流動式樣品槽中以不同波長紫外光光解碘甲烷類分子(CH3I, CH2I2, CHI3, CH2ICl)與溴甲烷類分子(CHBr3, CHBr2Cl)，調查其初始放光光譜中高激發態鹵素原子之形成機制，以釐清在過去的研究中碘原子與溴原子在生成機制上之不同。本研究經由改善實驗條件取得訊號更佳的高激發態溴原子放光光譜，因此發現到許多先前未觀測到之更高能階譜線，並以不同波長紫外光光解鹵甲烷類分子，發現高激發態溴原子要在光解波長短於273.5 nm才會產生，而且溴化甲烷類分子的趨勢一致。而高激發態碘原子則在光解波長短於276.5 nm會產生外，另外在光解波長298 nm有一共振帶會產生，所有碘化甲烷類分子有著相同的趨勢。基於本實驗的結果可推論，高激發態鹵素原子生成機制為步進式(step-by-step)吸收三光子的過程，並可能經共同反應中間物如鹵化亞甲基分子(CHX或CX2)而產生。

This work investigates the nascent emission spectra following the photolysis of iodomethanes (CH3I, CH2I2, CHI3, and CH2ICl ) and bromomethanes (CHBr3 and CHBr2Cl) at different ultraviolet wavelengths in a slow flow system at ambient temperature, and aims to resolve the discrepancy in the formation mechanisms of highly exited halogen atoms in previous studies. We have improved the experimental conditions for better atomic bromine signals and found several newly observed excited states. The photolysis of bromomethanes at different ultraviolet wavelengths shows a threshold wavelength at 273.5 nm for all bromomethanes, whereas the similar study of iodomethanes shows a threshold wavelength at 276.5 nm and a resonant band at approximately 298 nm for all iodomethanes. Based on our data, the highly excited halogen atoms are generated from a three-photon step-by-step process via a common reaction intermediate such as halomethylene (CHX or CX2).

1. Molina, M. J.; Rowland, F. S. Stratospheric Sink For Chloroflurormethanes : Chlorine Atomic-Atalysed Destruction of Ozone. Nature 1974, 249, 810.
2. Barrie, L. A.; Bottenheim, J. W.; Schnell, R. C.; Crutzen, P. J.; Rasmussen R. A. Ozone Destruction and Photochemical Reactions at Polar Sunrise in the Lower Arctic Atmosphere. Nature 1988, 334, 138.
3. Moore, R. M.; Webb, M.; Tokarczyk, R. Bromoperoxidase and Iodoperoxidase Enzymes and Production of Halogenated Methanes in Marine Diatom Cultures. J. Geophys. Res 1996, 101, 20899.
4. Chameides, W. L.; Davis, D. D. Iodine : Its Possible Role in Troposheric Photochemistry. J. Geophys. Res 1980, 85, 7383.
5. Holscher, D.; Zellner, R. LiF Study of the Reactions of the IO Radical with NO and NO2 over an Extended Range of Temperature and Pressure. Phys. Chem. Chem. Phys. 2002, 4, 1839.
6. Carpenter, L. Iodine in Marine Boundary Layer. J Chem. Rev. 2003, 103, 4953.
7. Saiz-Lopez, A.; Plane, J. M. C.; Baker, A. R.; Carpenter, L. J.;
von Glasow, R.; Gomez Martin, J. C.; McFiggans, G.; Saunders, R. W. Atmospheric Chemistry of Iodine. Chem. Rev. 2012, 112, 1773.
8. McGivern, W. S.; Sorkhabi, O.; Suits, A. G.; Derecskei-kovacs, A.; North, S. W. Primary and Secondary Processes in the Photodissociation of CHBr3. J. Phys. Chem. A 2000, 104, 10085.
9. Petro, B. J.; Tweeten, E. D.; Quandt, R. W. Dispersed Fluorescence and Computational Study of the 2 × 193 nm Phtodissociation of CHBr3 and CBr4. J. Phys. Chem. A 2004, 108, 384.
10. Chikan, V.; Fournier, F.; Leone, S. R.; Nizamov, B. State-Resolved Dynamics of the CH(A2Δ) Channels from Single and Multiple Photon Dissociation of Bromoform in the 10−20 eV Energy Range. J. Phys. Chem. A 2006, 110, 2850.
11. Ibuki, T.; Hiraya, A.; Shobatake, K. Vacuum ultraviolet absorption spectra and photodissociative excitation of CHBr2Cl and CHBrCl2. J. Chem. Phys. 1992, 96, 8793.
12. Taketani, F.; Takahashi, K.; Matsumi, Y. Quantum Yields for Cl (2Pj) Atom Formation from the Photolysis of Chlorofluorocarbons and Chlorinated Hydrocarbons at 193.3 nm. J. Phys. Chem. A 2005, 109, 2855.
13. Riely, S. J.; Wilson, K. R. Excited fragments from excited molecules: energy partitioning in the photodissociation of alkyl iodides. Discuss. Faraday Soc. 1972, 53, 132.
14. Kroger, P. M.; Demou, P. C.; Riley, S. J. Polyhalide photofragment spectra. I. Two‐photon two‐step photodissociation of methylene iodide. J. Chem. Phys. 1976, 65, 1823.
15. Senapati, D.; Kavita, K.; Das, P. K. Photodissociation Dynamics of CH2ICl at 222, 236, 266, 280, and~ 304 nm. J. Phys. Chem. A 2002, 106, 8479.
16. Chen, S. Y.; Tsai, P. Y.; Lin, H. C.; Wu, C. C.; Lin, K. C.; Sun, B. J.; Chang, A. H. H. I2 Molecular Elimination in Single-Photon Dissociation of CH2I2 at 248 nm by Using Cavity Ring-Down Absorption Spectroscopy. J. Chem. Phys. 2011, 134, 034315.
17. Cartoni, A.; Bolognesi, P.; Fainelli, E.; Avaldi L. Photofragmentation Spectra of Halogenated Methanes in the VUV Photon Energy Range. J. Chem. Phys. 2014, 140, 184307.
18. Cartoni, A.; Casavola, A. R.; Bolognesi, P.; Borocci, S.; Avaldi, L. VUV Photofragmentation of CH2I2 : The [CH2I–I]•+ Iso-diiodomethane Intermediate in the I-Loss Channel from [CH2I2]•+. J. Phys. Chem. A 2015, 119, 3704.
19. 陳政仲，國立中央大學化學系碩士論文(2006)。
20. 詹宗翰，國立中央大學化學系碩士論文(2007)。
21. 戴建弘，國立中央大學化學系碩士論文(2008)。
22. Yang, S. X.; Hou, G. Y.; Dai, J. H.; Chang, C. H.; Chang, B. C. Spectroscopic Investigation of the Multiphoton Photolysis Reactions of Bromomethanes (CHBr3, CHBr2Cl, CHBrCl2, and CH2Br2) at Near-Ultraviolet Wavelengths. J. Phys. Chem. A 2010, 114, 4785.
23. 劉振男，國立中央大學化學系碩士論文(2010)。
24. 楊欣樺，國立中央大學化學系碩士論文(2011)。
25. 朱致賢，國立中央大學化學系碩士論文(2014)。
26. Tu, C. P.; Cheng, H. I; Chang, B. C. Spectroscopic Study of the I2 Formation from the Photolysis of Iodomethanes (CHI3, CH2I2, CH3I, and CH2ICl) at Different Wavelengths. J. Phys. Chem. A 2013, 117, 13572.
27. 杜倩萍，國立中央大學化學系碩士論文(2013)。
28. Moore, C. E. Atomic Energy Levels, Natl. Bur. Stand. (U.S) Circ.467,Vol.III (1958); reprinted as Natl. Stand. Ref. Data. Ser., Natl. Bur. Stand. (U.S) 35, 1971.
29. Olney, T. N.; Cooper, G.; Brion, C. E. Quantitative Studies of the Photoabsorption (4.5 – 488 eV) and Photoionization (9 – 59.5 eV) of Methyl Iodide Using Dipole Electron Impact Techniques. Chem. Phys. 1998, 232, 211.
30. Seetula, J. A. Kinetics of the R + HBr → RH + Br(R = CH2I or CH3) Reaction. An Ab Initio Study of the Enthalpy of Formation of the CH2I, CHI2 and CI3 Radicals. Phys. Chem. Chem. Phys. 2002, 4, 455.
31. Kolesov, V. P. Russ. Thermochemistry of Halogenomethanes. Chem. Rev. 1978, 47, 599.
32. Seetula, J. A.; Russell, J. J.; Gutman D. Kinetics and Thermochemistry of the Reactions of Alkyl Radicals (Methyl, Ethyl, Isopropyl, Sec-butyl, Tert-butyl) with Hydrogen Iodide :
a Reconciliation of the Alkyl Radical Heats of Formation. J. Am. Chem. Soc. 1990, 112, 1347.
33. David R. Lide, Editor, CRC Handbook of Chemistry and Physics student edition, 76th ed. (CRC Press, New York, 1995).
34. Shuman, N. S.; Zhao, L. Y.; Boles, M.; Baer, T. Heats of Formation of HCCl3, HCCl2Br, HCClBr2, HCBr3, and Their Fragment Ions Studied by Threshold Photoelectron Photoion Coincidence. J. Phys. Chem. A 2008, 112, 10533.
35. NIST Chemistry Webbook, http://webbook.nist.gov/chemistry/.
36. Huang, H. Y.; Chuang, W. T.; Sharma, R. C.; Hsu, C. Y.; Lin, K. C. Molecular Elimination of Br2 in 248 nm Photolysis of Bromoform Probed by Using Cavity Ring-Down Absorption Spectroscopy.
J. Chem. Phys. 2004, 121, 5253.
37. Espinosa-García, J.; Db, S. Theoretical CH Bond Dissociation Enthalpies for CH3Br and CH2ClBr. J. Phys. Chem. A 1999, 103, 6387.
38. Wei, P. Y.; Chang, Y. P.; Lee, Y. S.; Lee, W. B.; Lin, K. C. Br2 Molecular Elimination in 248nm Photolysis of CHBr2Cl by Using Cavity Ring-Down Absorption spectroscopy. J. Chem. Phys. 2007, 126, 034311.
39. Song, Y.; Qian, X.-M.; Lau, K.-C.; Ng, C. Y.; Liu J.; Chen W. High-Resolution Energy-Selected Study of the Reaction CH3X+ → CH3 + X : Accurate Thermochemistry for the CH3X / CH3X+ (X = Br, I) System. J. Chem. Phys. 2001, 115, 4095.
40. Gillotay, D.; Jenouvrier, A.; Coquart, B.; Merienne, M. F.;
Simon, P. C. Ultraviolet Absorption Cross-Sections of Bromoform in the Temperature Range 295-240K. Planet. Space Sci. 1989, 37, 1127.
41. Bilde, M.; Wallington, T. J.; Ferronato, C.; Orlando, J. J.;
Tyndall, G. S.; Estupinan, E.; Haberkorn, S. Atmospheric Chemistry of CH2BrCl, CHBrCl2, CHBr2Cl, CF3CHBrCl, and CBr2Cl2. J. Phys. Chem. A 1998, 102, 1976.
42. http://satellite.mpic.de/spectral_atlas/index.html
43. Chang, B. C.; Costen, M. L.; Marr, A. J.; Ritchie, G.; Hall, G. E.;
Sears, T. J. Near-Infrared Spectroscopy of Bromomethylene in a Slit-Jet Expansion. J. Mol. Spectrosc. 2000, 202, 131.