【作者】 张帅；

【导师】 刘林华；

【作者基本信息】 山东大学 ， 动力工程及工程热物理， 2023， 硕士

【摘要】 MgO及CN分子光谱辐射参数在辐射场建模、天文探测及星际尘埃演化等过程中起重要作用。由于实验测量仅能得到分子基态及低激发态之间的光谱参数,为获取更全面的光谱数据,理论计算成为一种重要研究手段。作为重要光谱参数之一,吸收截面对于解决辐射吸收、散射和传输等问题都具有十分重要的作用,进一步考虑电子态之间耦合效应对吸收截面的影响可以为吸收截面的准确性提供重要保障,对实际工程应用具有重要意义。本文采用“从头算”方法,对MgO及CN分子的电子结构展开了理论研究,旨在得到MgO分子束缚-自由跃迁过程以及CN分子束缚-束缚跃迁过程的吸收截面。通过引入高激发电子态及耦合效应,进而得到更全面、准确的吸收截面,为实际工程应用提供更可靠的理论参考。本文主要工作如下:(1)从MgO及CN分子的微观结构出发,采用量子化学计算方法对MgO和CN的电子结构进行了精确计算。论文分别采用aug-cc-pVQZ及aug-cc-pwCV5Z-DK基组,计算了 MgO及CN分子基态、低激发态和高激发态的势能曲线、偶极矩曲线及耦合曲线。结果表明,MgO分子1Π态之间及CN分子高激发态之间均存在强耦合作用。(2)基于耦合通道理论,对MgO分子开展了预解离过程的研究。本文采用直接交叉互换的方法,构造了非绝热势能曲线,建立了 MgO分子预解离相互作用矩阵,计算了 MgO分子通过1Π态发生预解离的吸收截面。结果发现,自旋轨道耦合效应在140～200 nm范围内对预解离截面影响很大。(3)论文综合考虑自旋轨道耦合、轨道角动量耦合及非绝热效应,计算了CN分子束缚-束缚跃迁过程的吸收截面,分析了非绝热效应对吸收截面的影响。此外,基于高斯线型,计算了 T=1000 K下的吸收截面;基于洛伦兹线型,计算了 T=2000 K下的吸收截面,研究发现,耦合效应在计算的整个波数范围内对吸收截面均有影响。(4)论文以X ~2∑~+-X ~2∑~+及X~2∑~+-A 2Π跃迁过程为研究对象,分别计算了基于洛伦兹线型,在T=300K、1000K、3000K以及8000K下的吸收截面数据,为实际应用提供理论参考。更多还原

【Abstract】 The spectral radiation parameters of the MgO and CN molecules play an important role in radiation field simulations,astronomical surveys and the evolution of interstellar dust.Since experimental measurements only yield spectral parameters between the ground and low-lying excited states of the molecule,theoretical calculations become an important research tool in order to obtain more comprehensive spectral data.As one of the most important spectral parameters,the absorption cross section plays an important role in solving problems of radiation absorption,scattering and transmission.Further consideration of the effect of coupling effects between electronic states on absorption cross sections can provide an important guarantee for the accuracy of absorption cross sections,which is of great significance for practical engineering applications.In this thesis,based on ab initio method,a theoretical study of the electronic structure of MgO and CN molecules was carried out,aiming to obtain the absorption cross section for the bound-free transition process of MgO and the bound-bound transition process of CN,and by introducing the highly excited electronic states and coupling effect,more comprehensive and accurate absorption cross section was calculated for practical engineering applications.This paper provided a more reliable theoretical reference for practical engineering applications.The main work of this paper is as follows:(1)From the microstructure of MgO and CN molecules,the electronic structures of MgO and CN have been accurately calculated using quantum chemical calculations.The potential energy curves,dipole moment curves and coupling curves of the ground,low and highly excited states of MgO and CN molecules were calculated with aug-ccpVQZ and aug-cc-pwCV5Z-DK basis sets,respectively.The results show that there is strong coupling between the 1Π state of MgO molecules and between the high excited states of CN molecules.(2)Based on the coupled-channel theory,the predissociation process of MgO molecules has been studied.In this paper,a non-adiabatic potential energy curve was constructed,the interaction matrix of the MgO molecule for the calculation of predissociation process was established,the absorption cross section of the MgO molecule predissociation through the 1Π state was calculated,and the spin-orbit coupling effect was found to have a significant influence on the pre-dissociation cross section in the 140～200 nm range.(3)In the thesis,the absorption cross section of the CN molecule bound-bound transition process was calculated by considering spin-orbit coupling,orbital angular momentum coupling and non-adiabatic effects,and the influence of non-adiabatic effects on the absorption cross section was analyzed.In addition,the absorption cross section at T=1000 K was calculated based on Gaussian lines,and the absorption cross section at T=2000 K was calculated based on Lorentzian lines,and it was found that the coupling effect has an effect on the absorption cross section over the entire range of wave numbers calculated.(4)This thesis took the X ~2∑~+ X ~2∑~+and X ~2∑~+-A 2 Π transition processes for example and presented the data of absorption cross section with Lorentzian lines at T=300 K,1000 K.3000 K and 8000 K,respectively to provide a theoretical reference for practical applications.更多还原