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Vacuum Ultraviolet Mass-analyzed Threshold Ionization (VUV-MATI) Spectroscopy of Trimethylacetaldehyde

Title
Vacuum Ultraviolet Mass-analyzed Threshold Ionization (VUV-MATI) Spectroscopy of Trimethylacetaldehyde
Authors
김경은
Issue Date
2017
Department/Major
대학원 화학·나노과학과
Publisher
이화여자대학교 대학원
Degree
Master
Advisors
김명화
Abstract
We selectively report the vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectrum of trimethylacetaldehyde ((CH3)3CCHO) by varying the supersonic expansion conditions with the vapor pressure of the sample and the carrier gases. At first, we carefully measured the vacuum ultraviolet photoionization efficiency (VUV-PIE) curve to figure out the 0-0 peak in the vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectrum, which is basically the origin band for the vibrational spectrum of the cation. We obtained the high-resolution one-photon MATI spectrum of the using the VUV pulse generated by four wave difference frequency mixing in Kr cell and definitely determined the ionization energy of trimethylacetaldehyde to be 76625 ± 6 cm-1, based on the VUV-PIE curve. We then assigned the peaks observed in the VUV-MATI spectrum of trimethylacetaldehyde by utilizing the Franck-Condon factors and the frequencies calculated through fitting the geometry with an aid of the density functional theory (DFT) calculation performed at the wB97XD/cc-pVTZ level. Based on good agreement between the experimental and calculated results, we determine the definite cationic structure of trimethylacetaldehyde with the Cs symmetry in the ground electronic state.;우리는 초음속 팽창을 이용해 trimethylacetaldehyde ((CH3)3CCHO)의 진공 자외선 질량 분석 문턱 이온화 (VUV-MATI) 스펙트럼을 선택적으로 얻었다. 크립톤을 이용한 사 파장 차 혼합법으로 고해상도 단 광자 VUV-MATI 스펙트럼을 얻었다. VUV-PIE를 측정해 얻은 0-0 band의 위치를 기반으로 trimethylacetaldehyde 의 이온화 에너지를 76625 ± 6 cm-1로 결정했다. DFT 계산을 wB97XD / cc-pVTZ 수준에서 수행하였고 이를 이용해 Franck-Condon factor를 계산하였으며 이를 통해 진동 스펙트럼에 나타난 trimethylacetaldehyde의 진동 모드를 배정하였다. 중성 분자와 양이온의 구조를 정확하게 결정하기 위하여 Franck-Condon fitting을 수행하였고 양이온으로 변할 때의 구조 변화를 알 수 있었다. Trimethylacetaldehyde는 바닥 상태 양이온에서의 구조는 Cs 대칭을 갖는다.
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