Theoretical Study On Electronic Structures And Spectroscopic Properties Of Diatomic Molecules Containing C And Ge Atom And Their Ions

The diatomic molecules containing carbon atoms and germanium atoms play animportant role in astrophysical physics and semiconductor thin film field. Thespectra of CS have been observed in astrophysical environments. CS is also viewedto be related to formation of acid rain, and can lead to stratospheric ozone depletionand global climate change. CS and its isovalent molecular CSe are potential workingmedium for a mid-infrared CO chemical laser, which can be produced through O+CS(CSe)â†'CO*+S(Se) reactions. Understanding the branching processes in thereaction mixture needs the detailed information on the electronic structures andspectroscopic properties of excited states of CS and CSe. Previous investigationsindicated that CS and CSe have large state density, and the coupling interactionsbetween excited states could affect the electronic structures and dissociationdynamics of excited states, leading to difficulties in analysis of spectra and lack ofinformation on the spectroscopy of the two molecules. Hence, there is an urgentneed of theoretical work that provides the information on the electronic structuresand spectroscopic properties of excited states of the two molecules. In the process ofgrowth of semiconductor thin film containing Ge atom, GeH and GeH+areimportant intermediates. The information of the spectroscopy properties ofGeH/GeH+can provide support for monitoring the process of growth of semiconductor thin film, and improving production efficiency. A Ge atom has largeatomic number, and the spin-orbit coupling splitting of Ge atom is larger than550cm-1. Hence, the evident spin-orbit coupling effect of GeH can lead topredissociation of some electronic states, which causes the diffuseness of spectra ofexcited states. As a result, the reassignment of these spectra and fitting thespectroscopic parameters of these excited states are difficult. Fortunately, theoreticalwork can provide supporting information on the electronic structures and transitionalproperties of correlating excited states of GeH. In this work, the accurate electronicstructures of CS, CSe, GeH, and GeH+are calculated with high-level ab initiomethod, the dominant content are provided below.(1) The potential energy curves of Λ-S states of CS and CSe are calculatedusing a multireference configuration interaction method (MRCI), where theDavidson correction, the scalar relativistic effect, the spin-orbit coupling effect, andthe core-valence correlation effect are taken into account in the calculations. On thebasis of calculated potential energy curves of Λ-S states and states, thespectroscopic parameters of bound states are evaluated. With the aid of Λ-Scompositional variation of states, the influence of the spin-orbit coupling effect onthe electronic structure of electronic state is analyzed. The perturbation to thevibrational states of a3Π and A1Π states is analyzed via the values of the spin-orbitcoupling matrix near the avoided crossing points, illuminating the effect ofspin-orbit coupling on the the spectral intensity and radiative lifetimes. In short,we obtain the accurate electronic structures of CS and CSe, and our calculatedspectroscopic parameters of the two molecules agree well with previousexperimental results, and the calculated radiative lifetimes of CS are also inaccordance with the latest experimental results, indicating the reliability of ourcalculations.(2) The electronic structures of the ground state and excited states ofGeH/GeH+are calculated with the MRCI+Q method. The correlation effect of3dorbital of Ge atom and the relativistic effect (the scalar relativistic effect and thespin-orbit coupling effect) are also taken into consideration in the calculations. The potential energy curves of12Λ-S states/24states of GeH and8Λ-S states/23states of GeH+are obtained. On the basis of computed potential energy curves, thespectroscopic parameters of bound states are fitted. The electronic dipole momentsof Λ-S states are calculated, and the relationship between variation of electronicdipole moment and electronic configuration is analyzed. With the aid of calculatedspin-orbit matrix near the avoided crossing points, the possible predissociatedchannels of GeH are discussed, illuminating the influence of the coupling of theexcited states on the process of predissociation and spectra of excited states. Thetransition dipole moments, excitation energies, and the Franck-Condon factorsbetween the excited states and the ground state are calculated, and the radiativelifetimes of several low-lying states are obtained.