二硫化碳光譜與選擇性模態光分解研究

Abstract

本論文工作的主要研究課題，在於探討不同振動模態對分子進行光分解的影響。為了探討這個問題，我們選擇二硫化碳分子為研究對象，並利用(1)雷射誘發螢光光譜(Laser induced fluorescence detection)、(2)激發-探測螢光衰減光譜(Pump-Probe fluorescence depletion detection)、(3) 型激發光譜( Lambda-type excitation technique)、及(4)飛行時間式質譜(Time-of-Flight mass spectroscopy)等技術進行研究。 利用這些探測技術，本文之相關工作中對二硫化碳分子從事光譜研究與分析。研究內容包括：(1)利用「激發-探測螢光衰減光譜技術」，這種雙光子共振激發過程，對二硫化碳分子於真空紫外光(VUV)能量範圍的能態進行研究。實驗中發現三個能帶譜線，依據譜線並利用群論對作對稱性分析，推論此三個能帶屬於3(Pi)g 電子態。(2)利用「

In these studies, we were interested in the topic of “mode-selected photo-dissociation”. For this goal, CS2 molecule was chosen for our studies and a series of spectroscopic techniques including 1) laser induced fluorescence detection, 2) pump-probe fluorescence depletion detection, 3) Lambda -type excitation technique, and 4) time-of-flight mass spectroscopy were applied. Using these spectroscopic techniques, we have studied the CS2 molecule in vibrational and rotational details. Our research includes: 1) Using two-photon resonance excitation process, pump-probe fluorescence depletion detection technique, we investigate the spectroscopy of CS2 in VUV region. Three energy bands were observed, and they are assigned to be the outcome from 3(Pi)g electronic state which is assigned by symmetry argument of group theory to the spectra. 2) Using -type excitation technique we reinvestigated the R-(1 8 0) group band of RB2 electronic excited state. By taking advantage of the -type excitation technique, the spectra were greatly simplified to facilitate spectrum analysis and assignment. More rotational data was recorded than previous published study, and more accurate molecule constant was obtained. Due to the high spectrum resolution of -type excitation technique, we have also observed two extra bands which probably provide key information for understanding the change from bending to linear geometry of CS2 in RB2 electronic state. Finally, combining all those spectroscopic techniques, we investigated the topic of “mode-selected photo-dissociation”. Molecules in ground vibrational state were transferred to each selected highly vibrational state of electronic state by using -type excitation techniques and than excited to common pre-dissociation state for further dissociation. A TOF mass spectrometer was set up to detect ions fragments. Due to the high spectroscopy resolution of -type excitation technique, spectra were rotational resolved, and line-width can be well determined for further dissociation rate estimation. The experiment results show that dissociation rate varies with vibrational modes of molecule before it dissociate. This gives a new direction for the study of dissociation dynamics.