【作者】 韩永昌；

【导师】 丛书林；

【作者基本信息】 大连理工大学 ， 原子与分子物理， 2009， 博士

【摘要】 随着脉冲激光技术的发展,超快超强脉冲激光越来越多地被用来控制光化学反应。从理论上研究在超快超强激光场作用下的原子和分子动力学具有重要的意义。对于求解原子和双原子分子等这类少体问题,使用基于求解含时Schr（o|¨）dinger方程的量子波包方法能够详细地描述系统的时变动力学过程,因此它被广泛地应用于分子反应动力学研究中。本论文基于量子含时波包方法来研究双原子分子在飞秒激光场中的动力学过程,探索利用飞秒激光脉冲控制化学反应的方法。主要工作包括以下几个方面:（1）使用一维含时波包模型,计算并讨论了NO分子里德堡态C²Π和价态B²Π之间的非绝热相互作用对C²Π←X²Π吸收光谱的影响。从激发态波包随时间的演化过程可以看出,波包的一部分在里德堡态C²Π上演化而另一部分则被束缚在价态B²Π上。结果表明,C²Π和B²Π之间的相互作用会影响到C²Π←X²Π吸收谱峰的强度和位置。C²Π态上v′=0,1,2的吸收谱峰发生红移,而v′=3,4,5的峰发生蓝移。（2）以Na₂分子为例,讨论了利用电离连续态作为中间态实现激光控制分子布居转移的可行性。首先使用一维含时波包模型,研究了激光强度、延迟时间、失谐对布居转移效率的影响。之后,将一维波包的计算结果与二维含时波包模型的结果进行比较,研究分子转动和分子取向对布居转移效率的影响。结果表明,尽管电离连续态对布居转移会产生一定损耗,同时分子转动也会在一定程度上降低布居转移效率,但是通过合理调节激光参数,仍然可以实现较高的布居转移效率。（3）以Br₂分子为例,提出了通过控制解离波包干涉来控制产物分支比的方案。两束泵浦光在解离势能面上先后产生两个解离波包,随着波包的演化,两个波包会发生干涉叠加。使用二维波包模型,计算并分析了解离产物在坐标和速度空间的径向分布以及速度角分布。结果表明,通过改变两束泵浦光的相位差以及延迟时间,可以控制分子光解离波包的干涉图样。同时,分子在不同解离通道中的解离几率也会发生不同程度的改变,进而产物分支比将会得到控制。（4）研究了NaI分子的非绝热光解离和光电离过程,提出了利用一阶非共振非微扰Stark效应来控制非绝热解离过程的方案。使用二维波包模型,分别研究了Stark控制脉冲的延迟时间、强度、频率和相位对非绝热解离动力学以及各通道解离几率的影响。结果表明,尽管在一阶非共振非微扰动力学Stark效应中,Stark能移方向在每个光周期内会改变两次,即两个透热态之间的能量差会以激光的频率来回地变大变小,但是利用一阶非共振非微扰动力学Stark效应,仍然可以实现对非绝热解离动力学的控制。通过调节Stark脉冲参数,可以很有效地实现对解离产物分支比控制,相应的结果可以从最终的光电子动能分布中反映出来。更多还原

【Abstract】 Along with the development of the laser pulse technology,the ultra-fast and ultra-intense laser pulses are used to control the photochemical reactions more and more extensively.Studying the interaction between ultra-fast and ultra-intense laser fields and atoms or molecules in theory is very necessary.For the solution of few-body problems such as interactions of atoms or diatomic molecules with laser fields,the time-dependent quantum wave packet method which is based on the solution of the time-dependent SchrSdinger equation,is an efficient way.Thus,it is widely used in the study of molecular reaction dynamics.The works in this thesis are based upon the time-dependent quantum wave packet method to study the dynamics of diatomic molecules in femtosecond laser fields,in order to make use of the femtosecond laser pulse to control the chemical reaction.The main works are as follows.（1） Using the one-dimension model,the effect of the nonadiabatic coupling between the Rydberg state C²Πand the valence state B²Πon the C²Π←X²Πabsorption spectrum of the NO molecule is calculated and discussed.From the evolution of the excited wave packet,it can be seen that one part of the excited wave packet travels on the Rydberg state C²Π,and the other part is trapped in the valence state B²Π.The coupling between C²Πand B²Πcan affect the absorption spectrum of C²Π←X²Πin spectrum intensities and peak locations.The peaks ofν′= 0,1,2 are shifted to the red and those ofν′= 3,4,5 are shifted to the blue.（2） The feasibility of steering molecular population transfer via ionization continuum is studied using the Na₂ molecule as an example.The effects of the intensity, delay and detuning of the laser pulse on the population transfer are discussed in detail based on the one-dimension model.The effect of molecular rotation and alignment on the population transfer is studied by comparing the one-dimension model with the two-dimension one.It is shown that although the ionization and the molecular rotation can decrease the population transfer efficiency to some extent,a large part of population transfer via ionization continuum can still be achieved by properly choosing the laser parameters.（3） An approach of controlling the dissociation product branching ratio of the Br₂ molecule is proposed based on the dissociating wave packet interference.Two pump pulses create dissociating wave packets interfering with each other.Using twodimension model,the radial distributions of dissociation products in coordinate and momentum space and the angular distribution are calculated and analyzed.It is shown that by varying the phase difference and delay time between the two pump pulses,the interference pattern of dissociating wave packets can be controlled and the dissociation probabilities in different dissociation channels can be changed to different degrees.（4） The nonadiabatic photodissociation and the following photoionization processes have been studied,using the NaI molecule as an example.Dissociation probabilities of different dissociation,channels and the branching ratio can be controlled by using the first order nonresonant nonperturbative dynamic Stark effect（DSE）.Using two-dimension model,the effects of the delay time,intensity,frequency and phase of the Stark pulse on the nonadiabatic dissociation dynamics and the dissociation probabihties are calculated.It is shown that although in this first order nonresonant nonperturbative DSE case,the Stark shift changes direction twice every laser period, i.e.,the energy difference between the two diabats can be enlarged and reduced backward and forward at the laser pulse carrier frequency,the nonadiabatic dissociation dynamics can be controlled by the first order nonresonant nonperturbative DSE.By choosing proper parameters of the Stark pulse,the dissociation product branching ratio can be efficiently Controlled,which can be reflected from the final photoelectron kinetic energy distributions.更多还原