紫外光光解碘甲烷類分子產生之高激發態碘原子之形成機制研究

朱致賢(Chu Chih Hsien)

指導教授 ： 張伯琛

國立中央大學/理學院/化學系/碩士(2014年)

摘要

本研究於室溫下流動式樣品槽中以紫外光光解碘化甲烷類分子(CH3I,
CH2I2, CHI3, CH2ICl)研究其放光光譜，因先前研究以266 nm 光解碘化甲烷
類分子時在12430 cm-1 (804.5 nm)發現有高激發態碘原子6p 4Po
3/2 → 6s 4P5/2之放光，但其形成機制卻有待釐清。本研究改善實驗條件取得高激發態碘原子之雷射功率對訊號強度的關係(power dependence)，結果顯示此碘原子為三個光子過程之產物。進一步以266 nm 光解碘化甲烷類分子(CH3I, CH2I2,CHI3, CH2ICl)並掃描其他波長，發現在11000-14000 cm-1 有數根高激發態碘原子的訊號，分析後發現這些高激發態碘原子大多來自不同上能階，但大多都是碘原子6p → 6s 的放光，並且在不同前驅物所得的碘原子在上能階的
分布有很大的差異。此外，樣品槽壓力與訊號強度的關係(pressure
dependence)及壓力與訊號上升時間的關係實驗皆證明此碘原子非碰撞產物，
而是碘化甲烷類分子吸收三個紫外光(波長短於300 nm)光子至高激發態後
光解分子而產生。

關鍵字

碘化甲烷類 ； 光解 ； 高激發態碘原子 ； 紫外光

並列摘要

Nascent emission spectra following the photolysis of iodomethanes (CH3I, CH2I2, CHI3, and CH2ICl) at ultraviolet wavelengths were recorded in a slowflow system at ambient temperature since an emission peak at 12430 cm-1 (804.5
nm) of atomic iodine emission 6p 4Po3/2 → 6s 4P5/2 was observed in previous studies, but its formation mechanism remains unclear. We have improved the experimental conditions for better signals and the power dependence
experiments of 266 nm photolysis of these iodomethanes indicate the formation of highly excited atomic iodine is a three-photon process. Additionally, several atomic iodine emission peaks were also found in the region of 11000-14000 cm-1.Most of these peaks correspond to the 6p → 6s emission with different upper states and different population distributions. Based upon the time-resolved spectroscopy and pressure dependence experiments, the formation of highly
excited iodine atoms is not collisional. The formation mechanism is a three-photon process (λ< 300 nm), which excites the iodomethanes to a highly excited state and the following photodissociation produces the highly excited
atomic iodine.

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