Theoretical description of the electron continuum spectrum in polyatomic molecules: Application to angular-resolved electron and fluorescence spectroscopy

提出了计算多原子分子中电子连续谱的单中心方法，并用计算机代码实现。在该方法中，一个单粒子分子轨道是相对于分子的单一中心，通过膨胀的球形谐波表示。我们提出了该方法的两种表述。在稳态SC方法中，寻找光电子的波函数作为径向偏波的耦合Hartree-Fock方程组的数值解。SC方法的时间相关公式（TDSC）是非扰动地解释了电子与外场的相互作用，包括在强激光脉冲存在下的有效分子势中单活性电子波包的直接传播。通过计算小簇簇的微分光离截面对该方法进行了验证，并应用于解释了我们合作伙伴用不同的多原子分子进行的几个角分辨光离实验。特别地，我们研究了N2O、CO2和CH3Cl分子在内壳激发后的共振俄歇衰变（以及随后的荧光发射）中不同类型的干涉效应。它还被用来揭示一种新的“衰变速率借用”机制，即通过核与里德堡激发的CH4分子中的振动耦合。最后，SC方法从理论上解释了单轴取向的甲基氧乙烷c3h60和随机取向的三氟甲基氧乙烷c3h3f30分子内壳电离后光电子角分布的圆二色性。在第二阶段，我们计划将SC方法应用于分子中电子和荧光发射的新角分辨实验的理论解释。拟议的理论研究将与我们的实验伙伴合作进行。我们将一起讨论几个基本的物理问题，这些问题可以用角分辨率来澄清。具体来说是：(1)固定空间CO2分子内壳层光离中o1s电子的定位；（ii） CO分子激发和级联衰变后荧光光谱呈现圆二色性；（iii）电子态干扰定向N2O分子的O - k边共振俄歇衰变，以及在其Cl L2,3边以下自由旋转的CH3Cl分子的激发和衰变。我们还计划对H2O和N2O分子的不同电子轨道的角分辨光离进行系统的理论研究。

Single Center (SC) method for the calculation of the electron continuum spectrum in polyatomic molecules is developed and implemented in computer codes. In the method, a one-particle molecular orbital is represented with respect to a single center of the molecule via an expansion in terms of spherical harmonics. We developed two formulations of the method. In the stationary SC method, wave functions of a photoelectron are sought as the numerical solutions of the system of coupled Hartree-Fock equations for the radial partial waves. The time-dependent formulation of the SC method (TDSC) accounts for the interaction of electrons with external field nonperturbatively and consists in the direct propagation of single-active-electron wave packets in the effective molecular potentials in the presence of intense laser pulses. The method was tested by computing the differential photoionization cross sections of small Liclusters and applied to interpret several angular-resolved photoionization experiments with different polyatomic molecules, which were performed by our cooperation partners. In particular, we studied different types of interference effects in the inner-shell excitation followed by the resonant Auger decay (and subsequent fluorescence emission) in N2O, CO2, and CH3Cl molecules. It was also used to uncover a novel ‘decay rate borrowing’ mechanism via vibronic coupling in the core-to-Rydberg excited CH4 molecule. Finally, SC method enabled theoretical interpretation of experiments on the circular dichroism in angular distribution of photoelectrons emitted after inner-shell ionization of uniaxially oriented methyloxirane C3H6O and randomly-oriented trifluoromethyloxirane C3H3F3O molecules. In the second period, we plan to apply SC method to the theoretical interpretation of new angularresolved experiments on electron and fluorescence emission in molecules. The proposed theoretical studies will be performed in cooperation with our experimental partners. Together, we will address several fundamental physical questions, which can be clarified with the angular resolution. In particular, these are: (i) localization of the O 1s electron in inner-shell photoionization of fixed-in-space CO2 molecule; (ii) circular dichroism in the fluorescence spectra after excitation and cascade decay of CO molecule; (iii) electronic state interference in the O K-edge resonant Auger decay of oriented N2O molecule, and in excitation and decay of freely rotating CH3Cl molecule below its Cl L2,3-edges. We also plan a systematic theoretical study of the angular-resolved photoionization of different electronic orbitals of H2O and N2O molecules.