子計畫一:飛秒超強光雷射之研究; 子計畫二: 光化學的超快過程之研究

Abstract

近來我們利用雷射偏振性，研究對掌性分子環電流方向之量子控制，並發現伴隨的 振動光譜變化。而在理論層面，受限於需採用薛丁格方程式的數值解，只能考慮兩個振 動模式。我們計畫利用密度矩陣來處理量子控制問題，此方法可容納更多振動模式，並 可應用於處理其它量子控制問題。 在高功率雷射化學領域，S. L. Chin 等人觀察到惰性氣體原子與一氧化碳等分子的 居量陷俘現象。本計畫中我們利用廣義Keldysh 理論研究此問題，初步計算已獲致相當 良好的成果。 關於分子的高功率雷射游離─解離，母離子在外加雷射電場影響下能發生解離（100 飛秒之內）；解離亦能發生在雷射電場範圍之外。本計畫中我們研究第一種離子解離模 式，初步結果顯示取決於雷射強度（大於每平方公分1014 瓦），在飛秒時域中離子分解 非常明顯。 近來我們在吸收與螢光光譜、輻射性與非輻射性躍遷的第一原理量子化學計算獲得 諸多成果，包括典型分子如甲醛、苯、吡咯、嘧啶等之S1 → S0 生命期，理論與實驗結 果的一致性令人滿意。圓錐交點多年來引起相當程度重視，最近（2010 年）Suzuki 等人 利用20 飛秒雷射研究吡咯S2 電子態動力學，發現其生命期為22 飛秒。然而，雖然在光 電子訊號中觀察到量子拍現象，他們並未納入考慮以決定S2 電子態生命期。本計畫中我 們將採用密度矩陣方法，同時考慮居量與相干性，分析其實驗數據以正確決定S2 生命 期，也將建立處理圓錐交點之非輻射性過程理論。 最近Singh 等人利用埃秒脈衝列將D2 激發至D2 +，以時間延遲與紅外光來控制電子 定域化。本計畫中我們將利用密度矩陣方法來處理控制埃秒電子運動。

Keyword: quantum control, molecular chirality, ring currents, high-power laser, population trapping, field-assisted dissociation, first-principle calculation, photophysical processes, conical intersections, attosecond processes, density matrix, quantum coherence Part I Recently we have studied the quantum control of the direction of ring currents by polarization of lasers in a chiral molecule and found the accompanying changes of vibrational spectra. The theoretical method used is the numerical solution of Schrödinger equations. Because of this limitation, only two vibrational modes are considered. In this project we propose to employ the density matrix method to study the quantum control problems. Using this method not only more vibrational modes can be considered but also any other quantum control problems can be treated. In high-power chemistry, population trapping of inert gas atoms and molecules (e.g. CO) have been observed by S. L. Chin et al. In this project, we shall employ our generalized Keldysh theory to study this problem. Our preliminary calculation produces encouraging results. In high-power ionization–dissociation of molecules, the dissociation of ions can take place when the parent ions are still under the influence of the applied laser field (within 100 fs). The dissociation of ions can also take place outside the applied laser field. In this project we shall study the first type of dissociation of ions. Our preliminary investigations show that, depending on laser intensities (I > 1014 W/cm2), the ion dissociation in fs can be quite significant. Part II Recently we have succeeded in using the first-principle quantum chemical calculations of absorption and fluorescence spectra, and radiative and non-radiative transitions, that is, lifetimes of S1 → S0 for prototype molecules: formaldehyde, benzene, pyrazine, pyrimidine, etc. The agreement between experiment and theory is satisfactory. Conical intersections have attracted considerable attention for a number of years. Very recently (2010), Suzuki et al. have employed the 20 fs laser to study the dynamics of the S2 state of pyrazine and found the lifetime of S2 to be 22 fs. However, although they observed the quantum beat in their photoelectron signals, they did not take the quantum beat into their consideration to determine the S2-state lifetime. In this project we shall use the density matrix method which takes into account both population and coherence to analyze their data to determine the S2-state properly. We shall also develop a theory of radiationless process which can treat conical intersections. Recently Singh et al. have employed APT (attosecond pulse train) to pump D2 into D2 + and the time delays and IR were used to control the electron localization. In this project we shall employ the density matrix method to study of the control of attosecond electron motion.