서지주요정보
Photodissociation and multiphoton ionization dynamics using two-dimensional photofragment imaging technique = 이차원 광분열체 영상법을 이용한 광분해 및 다광자이온화 동역학에관한 연구
서명 / 저자 Photodissociation and multiphoton ionization dynamics using two-dimensional photofragment imaging technique = 이차원 광분열체 영상법을 이용한 광분해 및 다광자이온화 동역학에관한 연구 / Yong-Shin Kim.
저자명 Kim, Yong-Shin ; 김용신
발행사항 [대전 : 한국과학기술원, 1997].
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8007572

소장위치/청구기호

학술문화관(문화관) 보존서고

DCH 97004

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초록정보

Photodissociation of $CF_3I$ at 277 nm: The photodissociation of $CF_3I$ cooled in a supersonic molecular beam has been investigated at 277 nor by state-selective photofragment imaging. Fragmented iodine atoms of two spin-orbit states are state-selectively ionized and projected onto a two-dimensional position-sensitive detector, to obtain their speed and angular distributions. The anisotropy parameter for an excited iodine atom $I^*(^2P1/2)$, $β(I^*)$, is found to be 1.83 and is consistent with a dissociation lifetime in the order of 150 - 350 fs from rotational correlation function. Contrary to earlier reports, the parallel-like distribution for the ground state iodine atom $I(^2P3/2)$ at this wavelength, shows a more favorable curve-crossing dissociation path (68%) from $^3Q_0$ to $^1Q_1$ and a less favorable direct dissociation path (32%) from $^3Q_1$. The recoil energy distribution of I is found to be broader than that of $I^*$ and is correlated with a variety of energy disposal channels by an e symmetry vibration at the crossing point. The results are compared with previous works, and the strong photon energy dependence of the energy partitioning in $CF_3+I^*$ channel and curve crossing are interpreted in terms of the final state interaction and curve crossing probability, respectively. Photodissociation of t-Butyl Iodide at 277 and 304nm: The photo-dissociation of $t-C_4H_9I$ has been studied at 277 and 304 nm in a supersonic molecular beam. The fragments (I and $t-C_4H_9I$ radical) are selectively ionized by resonance-enhanced multiphoton ionization and then projected onto a two-dimensional position-sensitive-detector to obtain their translational energy and angular distributions. The energy distribution is found to consist of three components - one Boltzmann and two Gaussian distributions. Their anisotropy parameters range from 0.5 to 1.7 and display the parallel transition characteristic, where the greater the kinetic energy of the component the stronger its anisotropy. From present and previous works, these three components can be interpreted in terms of three independent reaction paths on an excited potential energy surface: (1) the prompt dissociation along the C-I stretching mode, (2) the repulsive mode along the C-I stretching, coupled with some bending motions, (3) the indirect dissociation, probably along a bounded reaction coordinate for the high-$E_t$ and the low-$E_t$ Gaussian, and the Boltzmann, respectively. Relative quantum yields for $I(^2P_3/2)$ at 277 and 304 nm have been determined and found to be 0.93± 0.03 and 0.92±0.04, respectively. Experiments have shown that $t-C_4H_9I$ has the highest curve-crossing probability from $^3Q_0$ state to $^1Q_1$ among alkyl iodides. The extensive vibrational coupling between two states in the proximity of a crossing point supports this interpretation. Photodissociation of IBr Near 267 nm: The photodissociation dynamics of IBr has been investigated near 267 mn by two-dimensional photofragment imaging technique. Speed and angular distributions for $Br(^2P_3/2$) and $Br^*(2P_1/2)$ fragments are obtained from the center-stripe analysis of their images. Based on the speed distributions, three dissociation channels are observed and identified with the formations of $Br(^2P_3/2)+I(^2P_3/2)$, $Br^*(2P_1/2)_I(^2P_3/2)$, and $Br(^2P_3/2)+I^*(^2P_1/2)$. Although there is a difference in contribution, these three paths are found to have the mixed character of parallel and perpendicular transition judging from the values of their anisotropy parameters. Relative quantum yields for the three channels are determined and then resolved into transition types from their anisotropies. Combined with the recent work at 304 mn [Jung, Griffiths, and El-Sayed, J. Chem. Phys. 103, 6999 (1995)1 our results present the complete assignment of the photoexcitation leading to the three channels in the UV band region: predominantly the perpendicular transition to $^1Π_1(2341)$ state, mainly the parallel $^3Π_0+(2341)$ transition, and the mixed one to the parallel $^3Π_0+(2341)$ and/or $^3∑^-_0+(2422)$ and perpendicular $^3Π_1+(2341)$ states for $I+Br^*$, $I^*+Br$, and I+Br channels, respectively. From the change in the relative quantum yield according to excitation photon energy, nonadiabatic couplings and an order of vertical energy between excited states have been discussed. '2+1' REMPI of Iodine Atom: Photoelectron imaging technique is applied to study on '2+1' REMPI of iodine atoms produced from the A-band photolysis of $CH_3I$ in the wavelength region 277-313 nm. The technique provides a chance to obtain the relative branching ratios among possible ion states and their angular distributions of ejected photoelectrons, simultaneously. The branching ratios reveal a propensity toward core-preservation ionization. State-selective formation of $I^+(^3P_j)$ and $I^+(^1D_2)$ ions is possible at several resonant wavelengths. The photoelectron angular distributions show contributions from outgoing electrons with a maximum angular momentum, $l_max=2$.

서지기타정보

서지기타정보
청구기호 {DCH 97004
형태사항 xi, 153 p. : 삽도 ; 25 cm
언어 영어
일반주기 Appendix : A, Detail drawings of the 2-D product imaging system. - B, Inverse abel transformation
저자명의 한글표기 : 김용신
지도교수의 영문표기 : Kyung-Hoon Jung
지도교수의 한글표기 : 정경훈
수록 잡지명 : "Intracluster ion/molecule reactions within C$\rm F_3$H cluster system". International Journal of Mass Spectrometry and Ion Processes. Elsevier Science B.V., vol. 135, pp. 119-128
수록 잡지명 : "Two-dimensional photoelectron imaging of state-selected iodine atom by (2+1) resonance-enhanced multiphoton ionization". Chemical Physics Letters. Elsevier Science B.V., vol. 244, pp. 183-187
수록 잡지명 : "State-selective photofragment imaging of iodine atoms via photodissociation of C$\rm F_3$I at 277 nm". Journal of Chemical Physics. American Institute of Physics, vol. 105, no. 2, pp. 551-557
학위논문 학위논문(박사) - 한국과학기술원 : 화학과,
서지주기 Reference : p. 114-119
주제 Photodissociation
Multiphoton ionization
Imaging technique
Iodine atom
Alkyl iodides
광분해
다광자이온화
영상기법
요오드원자
알킬아이오다이ong Shin
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