C_(∞v)对称分子在激光场中多光子激发的同位素效应

用二次量子化方法讨论了ＸＹ 分子在激光场中的多光子激发,包括对分子伸缩振动能级的计算,讨论了跃迁概率的长时间平均值和同位素效应     

HCl分子在激光场中的多光子激发

用二次量子化方法讨论了ＨＣｌ分子在激光场中的多光子激发，还包括对ＨＣｌ分子伸缩振动能级的计算，跃迁概率随外场频率的变化及随时间的变化（取光场强度１０~（－８）Ｗ／ｃｍ~２）。     

臭氧分子在激光场中的多光子激发

采用二次量子化方法和酉变换讨论了O3分子在激光场中的多光子激发.推导出了O3分子的振动Hamiltonian 算子、从基态到各激发态的跃迁几率公式,以及O3分子从激光场中吸收的光子数公式,并分析了计算结果.这包括对O3分子伸缩振动能谱的计算及与实验结果的比较,跃迁几率随外场频率的变化、随时间的变化,以及O3分子在辐射场中的能量吸收情况(取光场强度为5×10-2 W/cm2).建立讨论所有具有C2v对称分子从基态到第四激发态以下各态多光子激发问题的模型.     

用两束超短乜秒激光脉冲选择控制D2分子的转动波包

通过求解D2分子在飞秒激光场中的含时薛定谔方程,研究了室温下D2分子在超快1s秒激光驱动下的的转动波包动力学．选择用第一束超短飞秒脉冲与温度为300K的D2分子系综相互作用产生一个相干转动波包,用第二束超短匕秒脉冲在波包的1／4和3／4恢复周期选择操纵D2分子取向．研究结果表明,通过选择两束超短飞秒脉冲的延迟时间,可以有效控制D2分子转动波包中奇偶态的相对布居,从而选择性的控制D2分子取向．     

氨分子在激光场中的多光子激发

用二次量子化方法和酉变换讨论了NH_3分子在激光场中的多光子激发.这包括对NH_3分子伸缩振动能谱的计算,跃迁几率随外场频率的变化及随时问的变化.并讨论了能量吸收情况(取光场强度1.1×10~8 w/cm~2).     

强激光场中NO分子多光子选择激发──含时薛定鄂方程的代数解法

报道了在半经典偶极近似下应用二次型非谐振子李代数模型研究强激光场中NO分子的多光子选择激发，并计算了NO分子的跃迁几率．     

乙烯基~2A″电子态的振转分析

通过193nm光解丁烯酮分子产生乙烯基自由基(·C2H3).经射流冷却后,以另一束可调谐激光光解·C2H3,生成的氢原子碎片经共振增强多光子电离(REMPI)过程,记录氢离子信号随光解波长变化,得到21180￣21320cm-1范围内乙烯基A!2A″(!′5,6,8=1)←X!2A′(!″=0)跃迁的振转光谱.结合量化计算和光谱拟合,对该段光谱进行了细致的振转分析,确定了各振动谱带位置,识别了其中主要的转动跃迁.由光谱拟合得到各振动能级的预解离寿命,讨论了其与振动模式及激发转动量子数的依赖关系,证实了理论预测的乙烯基A!2A″电子态的面内解离机制.     

用质谱和光电子能谱研究飞秒强场中的电离动力学

报导了用自制飞秒激光器通过飞秒多光子电离质谱和光电子能谱对飞秒强激光场与分子（氨、苯）相互作用的研究。飞秒激光脉宽约100fs,二倍频中心波长407.5nm,聚焦后脉冲功率密度达到1012W/cm2。氨的光电子能谱显示了（2+2）REMPI和（2+2）+1ATI、（2+2）+2ATI三组电子峰,每组峰又包括伸缩振动v1的带系,ATI峰的振动布居出现反转。随着光强增加,谱峰加宽而且振动能级出现平移。这些强场效应可用PonderomotivePotential解释。苯的飞秒质谱图与纳秒情况不同,分子离子为主,碎片峰很少。     

乙烯基A2A″电子态的振转分析

通过193 nm光解丁烯酮分子产生乙烯基自由基(•C2H3). 经射流冷却后, 以另一束可调谐激光光解•C2H3, 生成的氢原子碎片经共振增强多光子电离(REMPI)过程, 记录氢离子信号随光解波长变化, 得到21180~21320 cm-1范围内乙烯基 A2A″(µ′5,6,8=1)←X2A′(µ″=0)跃迁的振转光谱. 结合量化计算和光谱拟合, 对该段光谱进行了细致的振转分析, 确定了各振动谱带位置, 识别了其中主要的转动跃迁. 由光谱拟合得到各振动能级的预解离寿命, 讨论了其与振动模式及激发转动量子数的依赖关系, 证实了理论预测的乙烯基A2A″电子态的面内解离机制.     

甲醇团簇的多光子电离质谱及其从头算

用355 nm激光对脉冲分子束超声膨胀冷却的甲醇分子进行多光子电离, 飞行时间质谱仪观测到除甲醇碎片离子外的质子化甲醇团簇(CH3OH)nH+(n=1-16), 且离子的种类及相对强度与激光相对于脉冲分子束的延时无关, 取决于团簇离子内在结构的稳定性. 结合从头算密度泛函理论, 在B3LYP/6-31G(d)基组水平上优化得到了(CH3OH)n和(CH3OH)nH+(n=1-4)的稳定构型. 振动频谱分析显示, 团簇中最强的红外振动模主要来自氢键H伸缩振动的贡献. 团簇电离后发生于团簇内的质子转移反应也可能与激光电离引起的与氢键有关的振动模激发密切相关.     

Rotational averaging and optimization of laser-induced population transfer in molecules

The dynamics of a molecule subject to a short laser pulse is investigated, with focus on the averaging over initial rotational states and on the optimization of laser parameters for the efficient population transfer between vibrational and electronic states. A relation is established between final-state populations obtained with a fixed orientation and those based on a full treatment of the rotational degrees of freedom. In the short-pulse approximation, rotational averaging amounts to integrating the fixed molecule results over all orientations. The theory is applied to a variety of model systems and verified with numerical calculations using Gaussian pulses. We calculate target state populations with three procedures, optimizing the laser pulse for a fixed orientation without orientational averaging, averaging without changing the laser parameters, and reoptimizing the parameters after averaging. The analysis of the two-level system provides a reference for the order of magnitude of the effects of averaging. The three-level system brings out the relevant role of the geometry of polarization vectors and transition dipoles. The multiphoton excitation of a Morse oscillator shows the importance of taking into account the dependence of resonance frequencies on the laser intensity. Within a proton transfer model we discuss the results obtained with and without chirping and we show that "optimizing after averaging" can be as effective as choosing a more refined pulse shape.     

Time-dependent Quantum Wave Packet Study of F+HCl and F+DCl Reactions

The F+HCl and F+DCl reactions are studied by the time-dependent quantum wave packet method, using the most recent potential energy surface reported by Deskevich et al.. Total reaction probabilities for a number of initial ro-vibrational states of HCl and DCl diatomic moiety are presented in the case of total angular momentum J=0. It is found that for both reactions the initial rotational excitation of the diatomic moiety enhances greatly the reaction probabilities but this e?ect is more signiˉcant for F+HCl system. This is mainly due to larger rotational constant of the HCl reagent. The initial vibrational excitation of the diatomic moiety has little e?ect on the reactivity for both systems except shifting down the collision energy threshold. The results indicate that the reaction coordinates for these two systems are e?ectively along rotational freedom degree. More quantum phenomena, such as tunneling and resonance, are observed in F+HCl reaction than F+DCl reaction, and for the initial states studied, the reactivity of the later is lower. Di?erent skewing angles of these two systems account for these isotopic di?erences.     

Effect of ro-vibrational excitation of HCl on the stereodynamics for the reaction of O(P) + HCl → OH + Cl

We have carried out quasi-classical trajectory calculations for the title reaction. The effect of initial ro-vibratioanl state of HCl on the stereodynamics of O(³P) + HCl → OH + Cl reaction on ³A″ potential energy surface was investigated. Integral cross sections, product ro-vibrational state distributions, differential cross sections, and three angle distribution functions about the products alignment and orientation have been presented. The results manifest that the vibrational excitation has a larger influence on the total cross section, differential cross section, angle distributions (concerning the initial/final velocity vector, and the product rotational momentum vector) compared with the rotational excitation, and the phenomena are quite different with the increase of the vibrational and rotational quantum number. Also the products are vibrationally cold and rotationally hot.     

A transition state view on reactive scattering: initial state-selected reaction probabilities for the H + CH4 → H2 + CH3 reaction studied in full dimensionality

Initial state-selected reaction probabilities for the H+CH(4)→H(2)+CH(3) reaction are computed for vanishing total angular momentum by full-dimensional calculations employing the multiconfigurational time-dependent Hartree approach. An ensemble of wave packets completely describing reactivity for total energies up to 0.58 eV is constructed in the transition state region by diagonalization of the thermal flux operator. These wave packets are then propagated into the reactant asymptotic region to obtain the initial state-selected reaction probabilities. Reaction probabilities for reactants in all rotational states of the vibrational 1A(1), 1F(2), and 1E levels of methane are presented. Vibrational excitation is found to decrease reactivity when reaction probabilities at equivalent total energies are compared but to increase reaction probabilities when the comparison is done at the basis of equivalent collision energies. Only a fraction of the initial vibrational energy can be utilized to promote the reaction. The effect of rotational excitation on the reactivity differs depending on the initial vibrational state of methane. For the 1A(1) and 1F(2) vibrational states of methane, rotational excitation decreases the reaction probability even when comparing reaction probabilities at equivalent collision energies. In contrast, rotational energy is even more efficient than translational energy in increasing the reaction probability when the reaction starts from the 1E vibrational state of methane. All findings can be explained employing a transition state based interpretation of the reaction process.     

Effect of diatomic molecular properties on binary laser pulse optimizations of quantum gate operations

The importance of the ro-vibrational state energies on the ability to produce high fidelity binary shaped laser pulses for quantum logic gates is investigated. The single frequency 2-qubit ACNOT(1) and double frequency 2-qubit NOT(2) quantum gates are used as test cases to examine this behaviour. A range of diatomics is sampled. The laser pulses are optimized using a genetic algorithm for binary (two amplitude and two phase parameter) variation on a discretized frequency spectrum. The resulting trends in the fidelities were attributed to the intrinsic molecular properties and not the choice of method: a discretized frequency spectrum with genetic algorithm optimization. This is verified by using other common laser pulse optimization methods (including iterative optimal control theory), which result in the same qualitative trends in fidelity. The results differ from other studies that used vibrational state energies only. Moreover, appropriate choice of diatomic (relative ro-vibrational state arrangement) is critical for producing high fidelity optimized quantum logic gates. It is also suggested that global phase alignment imposes a significant restriction on obtaining high fidelity regions within the parameter search space. Overall, this indicates a complexity in the ability to provide appropriate binary laser pulse control of diatomics for molecular quantum computing.     

Collisional relaxation of the three vibrationally excited difluorobenzene isomers by collisions with CO2: effect of donor vibrational mode

Relaxation of highly vibrationally excited 1,2-, 1,3-, and 1,4-difluorobenzne (DFB) by collisions with carbon dioxide has been investigated using diode laser transient absorption spectroscopy. Vibrationally hot DFB (E' approximately 41,000 cm(-1)) was prepared by 248 nm excimer laser excitation followed by rapid radiationless relaxation to the ground electronic state. Collisions between hot DFB isomers and CO2 result in large amounts of rotational and translational energy transfer from the hot donors to the bath. The CO2 nascent rotational population distribution of the high-J (J = 58-80) tail of the 00(0)0 state was probed at short times following the excimer laser pulse to measure rate constants and probabilities for collisions populating these states. The amount of translational energy gained by CO2 during collisions was determined using Doppler spectroscopy to measure the width of the absorption line for each transition. The energy transfer probability distribution function, P(E,E'), for the large DeltaE tail was obtained by resorting the state-indexed energy transfer probabilities as a function of DeltaE. P(E,E') was fit to a biexponential function to determine the average energy transferred in a single DFB/CO2 collision and fit parameters describing the shape of P(E,E'). P(E,E') fit parameters for DFB/CO2 and the previously studied C6F6/CO2 system are compared to various donor molecular properties. A model based on Fermi's Golden Rule indicates that the shape of P(E,E') is primarily determined by the low-frequency out-of-plane donor vibrational modes. A fractional mode population analysis is performed, which suggests that for energy transfer from DFB and C6F6 to CO2 the two key donor vibrational modes from which energy leaks out of the donor into the bath are nu11 and nu16. These "gateway" modes are some of the same modes determined to be the most efficient energy transfer modes by quantum scattering studies of benzene/He collisions.     

Sequential multiphoton ionization spectroscopy: extension of a useful spectroscopic tool

An adaptation of multiphoton ionization spectroscopy is presented in which a single vibrational—rotational level of an excited electronic state is pumped using a dye laser, and a second, independently tunable dye laser beam induces multiphoton ionization from this excited level. Several advantages of this technique are demonstrated using molecular iodine.