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學校名稱輔仁大學
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研究生(中)林柏伸
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論文名稱(中)HFCO 單分子反應的動力學和分子內振動能量的再分佈之研究
論文名稱(英)Detailed study of intramolecular vibrational energy redistribution and the unimolecular reaction dynamics of HFCO
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指導教授(中)柏殿宏
指導教授(英)Frank E. Budenholzer
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畢業學年度88
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關鍵字(中)古典軌跡計算 單分子hfco的解離反應
關鍵字(英)HFCO classical trajectory calculation
摘要(中)我們用古典軌跡的方法來研究HFCO單分子的解離反應。在我們的計算中所使用的位能面是由Budenholzer和Tsau Yu [J.Phys.Chem. A 1998, 102, 947]修飾了Wei and Wyatt的位能函數[J.Phys.Chem. 1993, 97, 13580]之後的結果,使用VENUS program來做古典軌跡的計算。 分子基本振動模式的零點能量為12.37 kcal/mol,我們對每一個激發模式增加約60 kcal/mol的能量,每一個模式計算3000個軌跡。由反應時間對相對應的ln(Nt/N0)作圖,其中Nt 為時間t時尚未反應的軌跡個數、N0為總軌跡數,我們可以得到dissociation lifetime τ。由HFCO的計算結果中,我們可以發現分別激發不同的基本振動模式(normal modes of vibrational),其解離反應的快慢為CH stretch> CH bend ≈ CF stretch>>CO stretch ≈ FCO bend > out of plane bend。經由dissociation lifetime (τ)的結果,我們發現在HFCO的反應中有著明顯的mode specificity,因為其out of plane bending mode的反應較其它modes慢了許多。在Choi and Moore[J.Chem.Phys. 1991,94,5414]的實驗亦有相似的情形。 對DFCO做類似於HFCO的軌跡計算。在DFCO中,其基本振動模式的反應快慢為CD bend ≈ FCO bend > CD stretch > CF stretch > out of plane bend > CO stretch。比較其lifetime後我們發現DFCO並無HFCO那麼明顯的mode specificity,而此一結果與Crane and co-workers [J.Phys.Chem. A 1998,102,943]的實驗結果相符。 為了更了解IVR在各個不同模式間的情形,我們針對15種不同的模式組合各計算了1000個軌跡。同時比較混合型式與單一型式反應速度的差異,an “enhancement coefficient” kab/[(ka+kb)/2],其中k為rate constant;當其值大於1時則混合模式的反應速度較各自的兩個模式為快,小於1時則慢,等於1時沒有影響。在激發混合振動模式(mixed mode excitation)的計算中,我們發現當CO stretch和CH bend混合激發時會增加反應的產生。Kamiya and Morokuma [J.Chem.Phys. 1991,94,7287]發現在反應的初期中CH bend和CF stretch間有較大的coupling,在剛要形成產物CO stretch and CH stretch和 CH stretch and CH bend這兩個組合都有較強的coupling。 我們也逐漸增加在起始環境下轉動能量(rotation energy)的值來做軌跡計算, 皆計算了1000軌跡數。同時亦計算比較其反應速率,發現除了out of plane bend的模式外,其於的振動模式在轉動能量剛增加時其反應速率常數卻減少。約當所增加的轉動能量到 60 kcal/mol之後才會較最初能量為0時大。但out of plane bend 有點不一樣的結果,我們推測其原因為rotation和out of plane bend間有較好的IVR。
摘要(英)We have carried out a classical trajectory calculation for HFCO, and its isotopomer, DFCO, using the potential energy surface from the work of Budenholzer and Tsau [J.Phys.Chem. A 1998,102,947], which is a modification of Wei and Wyatt’s surface function [J.Phys.Chem. 1993,97,13580]. We have used the VENUS program to calculate the classical trajectories. Trajectories were initiated with the classical zero point energy of 12.37 kcal/mol distributed randomly in the six normal modes of the molecule. Batches of 3000 trajectories were then run with an additional approximately 60 kcal/mol distributed in one of the six normal modes. The dissociation times of the trajectories were fit to an exponential decay curve and the decay constant τ=k-1 was determined. For HFCO, we can see that the mode excitation most likely leading to reaction is CH stretch> CH bend ≈ CF stretch>>CO stretch ≈ FCO bend > out of plane bend. Clear mode specificity is found in that the dissociation of the excitation of the out of plane bending mode is significantly slower than dissociation of excitation of the other modes. This result is agreement with the experimental results of Choi and Moore [J.Chem.Phys. 1991,94,5414]. Trajectories were run in a similar fashion for DFCO. The results for DFCO show that the dissociation of DFCO has less mode specificity than the dissociation of HFCO. The order of rate of reaction is CD bend ≈ FCO bend > CD stretch > CF stretch > out of plane bend > CO stretch. Our results seem to agree with the prediction of Crane and co-workers [J.Phys.Chem. A 1998,102,943]. They find significant IVR between the out of plane bending mode (υ6) and the CO stretching mode (υ2). To investigate the degree of IVR between various modes, 15 separate batches of 1000 trajectories were calculated with the same initial energy approximately equally divided between two different initial modes. To compare the rate constant for the mixed mode excitation with that of the two single mode excitations, an “enhancement coefficient” kab/[(ka+kb)/2] was calculated for each mixed mode rate constant, where kab=τab-1 is the first order rate constant for the mixed mode excitation. A value greater than one indicates that the mixed mode excitation enhances reaction over two single mode excitation. A value less than one indicates the opposite. A value of one indicates no overall effect. We find that the CO stretch combined with the CH bend gives the largest enhancement. Mixed mode results for the CO stretch and the CH stretch as well as for the CH stretch and the CH bend gave essentially no enhancement, either positive or negative. Kamiya and Morokuma carried out a theoretical calculation of mode coupling along the reaction coordinate [J.Chem.Phys. 1991,94,7287]. They found extensive coupling at the beginning of the exit channel between the CO stretch and the CH stretch and to a somewhat lesser extent between the CH stretch and the CH bend. Our results are consistent with this finding. Finally, batches of 1000 trajectories were calculated to study the effect of increasing rotational energy on the rate of HFCO dissociation. We find that the rate constant of dissociation decreases with the addition of the rotational energy, with the exception of the out of plane bending mode. For all modes, except the out of plane bend, the reactivity drops precipitously upon the addition of rotational energy. Only when the rotation energy is high, above 60 kcal/mol, does the rate constant of reaction will increase. The out of plane bending mode is the exception, we presume that rotation enhances IVR from the out of plane mode. Further study of these results is indicated.
論文目次Contents Abstract I、 Introduction -------------------------------------------------------------------------------- 1 II、 Method of calculation (1) Classical trajectory theory ---------------------------------------------------------- 4 a. The classical trajectory calculation --------------------------------------------- 4 b. The VENUS classical trajectory program --------------------------------------5 (2) The Potential Energy Surface -------------------------------------------------------7 a. Description of the potential energy surface ------------------------------------7 b. Energies and geometries of stationary structure of the HFCO system ----13 c. Normal mode analysis -----------------------------------------------------------17 (3) Trajectories ---------------------------------------------------------------------------20 (4) Calculation of the decay time ------------------------------------------------------34 III、Results and discussions ---------------------------------------------------------------- 48 (1) The Calculation of formyl fluoride, HFCO dissociation ---------------------- 48 (2) Isotope calculation, DFCO -------------------------------------------------------- 54 (3) Mixed mode excitation ------------------------------------------------------------ 60 (4) Adding the rotational energy ------------------------------------------------------ 65 V、 Conclusion ---------------------------------------------------------------------------- 72 VI、 References ---------------------------------------------------------------------------- 75 VII、 Appendix ------------------------------------------------------------------------------77
參考文獻Reference: 1. Choi, Y. S.; Moore, C. B. J. Chem. Phys. 1991, 94, 5414. 2. Choi, Y. S.; Moore, C. B. J. Chem. Phys. 1992, 97, 1010. 3. Choi, Y. S.; Moore, C. B. J. Chem. Phys. 1995, 103, 9981. 4. Wei, Tai-Guang; Wyatt, R. E. J. Phys. Chem. 1993, 97, 13580. 5. Budenholzer, F. E.; Tsau Y. J. Phys. Chem. A 1998, 102, 947. 6. Tsau, Yu. MS Dissertation, Fu Jen Catholic University, June 1996. 7. Crane, J. C.; Nam, H.; Clauberg, H.; Beal, H. P.; Kalinovski, I. J.; Shu, R. G.; Moore, C. B. J. Phys. Chem. A 1998, 102, 9433. 8. Baer, Michael. Theory of Chemical Reaction Dynamics. (Boca Raton, FL: CRC Press,1985) Sewell, T. D.; Thompson, D. L. “Classical Trajectory Methods for Polyatomic molecules,” International Journal of Modern Physics B, 1997, 9, 1067. 9. Hase, W. L.; Duchovi, R. J.; Hu, X.; Lim, K. F.; Lu, D.-h,; Peslherbe, G.; Samy, K. N.; Vande Linde, S. R.; Wolf, R. J. VENUS: A General Monte Carlo Classical Trajectory Computer Program; Quantum Chemistry Program Exchange 1966, 16, 671. 10. Hase, W. L.; Duchovi, R. J.; Hu, X.; Lim, K. F.; Lu, D.-h,; Peslherbe, G.; Samy, K. N.; Vande Linde, S. R.; Wolf, R. J. VENUS Manual. Quantum Chemistry Program Exchange 1966, 16, 671. Pp. 13-15. 11. Kamiya, K.; Morokuma, K. J. Chem. Phys. 1991, 94, 7287. 12. Green, W. H.; Jayatilaka, D.; Willetts, A.; Amos, R. D.; Handy, N. J. Chem. Phys. 1990, 93, 4965. 13. Goddard, J. D.; Schaeter, H. F., III J. Chem. Phys. 1990, 93, 4907. 14. Herzberg, G. Molecular Spectra and Molecular Structure; Volume III-Electronic Spectra of Polyatomic Molecules; Kriegier: Malabar, FL,1991; p614. 15. Yamamoto, T.; Kato, S. J. Chem. Phys. 2000, 112, 8006. 16. Yamamoto, T.; Kato, S. J. Chem. Phys. 1997, 107, 6114.
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