Theoretical Study On The Spectroscopic Properties Of The Excited States For The Phosphorus Monohalogen PX(X=Cl、Br、I、At) Molecules

The excited state phosphorus monohalogen molecules play an important role in the exploration and research of the novel chemical laser systems. The phosphorus monohalogen molecules, which is isoelectronic with O2, could be contribute to the form of a novel laser system, for the possibility of being expected as the working medium to interact with the iodine atom. The transition properties of the excited states determine that the phosphorus monohalogen molecules could be devoted to the gas-phase chemical storage. The phosphorus monohalogen molecules are the crucial intermediate in the etching of semiconductor devices. Accurately comprehending the structures of the electronic states and the spectroscopic properties are conducive to figure out the corresponding reaction mechanism. Therefore, the investigations on the excited states of the phosphorus monohalogen molecules are of great importance and significance. In our work, the high-level multi-reference configuration interaction(MRCI) method has been used to study the electronic structures and the spectroscopic properties of the excited states for the phosphorus monohalogen PX(X=Cl, Br, I, At) molecules. The main contents are as following:(1) The potential energy curves of the 34 Λ-S states for the phosphorus monohalogen PX(X=Cl, Br, I, At) molecules have been calculated by using the MRCI +Q method. The Davidson(+Q) correction has been taken into account to balance the size-consistency error. The calculated potential energy curves of the states indicate that the phosphorus monohalogen PX(X=Cl, Br, I, At) molecules have a high density region of electronic states. By solving the radial Schr?dinger equation, the spectroscopic constants of the bound states are determined. And the results are in good agreements with the previous experimental and theoretical spectroscopic results, which confirm the reliability of the calculation. The calculated results of dissociation energy De indicate that the potential well of the first excited a1Δ state is much deeper than that of the X3Σ- state. The analysis of wavefunction for the Λ-S states shows that the excited states of the phosphorus monohalogen PX(X=Cl, Br, I, At) molecules are multi-configurational in nature.(2) The state interaction method and the spin-orbit Breit-Pauli operator have been used to study the spin-orbit coupling effect of the phosphorus monohalogen PX(X=Cl, Br, I, At) molecules. With the aid of the calculated spin-orbit matrix elements, the interactings between the Λ-S states in the high density region of electronic states have been analyzed. And then the predissociations and the perturbations of the states are determined. At the same time, the spin-orbit matrix element also determines the splitting of the electronic states. And the electronic states of the heavier phosphorus monohalogen molecules have the larger energy splitting. Under the influence of the spin-orbit coupling effect, the 34 Λ-S states for the phosphorus monohalogen PX(X=Cl, Br, I, At) molecules split into 74 Ω states. The 3 Λ-S dissociation limits split into 10 Ω dissociation limits. The two Ω states are generated from the X3Σ- state, and the corresponding intervals for PCl, PBr, PI, PAt molecules are calculated to be 6cm-1, 21cm-1, 50cm-1, 174cm-1, respectively. The spin-orbit coupling effect brings the great influence to the dissociation relationships and dissociation energies of the a1Δ and b1Σ+ states. By the analysis of the wavefunctions for the Ω states, the main reasons are obtained.(3) The transition properties of the excited states for the phosphorus monohalogen PX(X=Cl, Br, I, At) molecules have been predicted. With the aid of the analysis of the wavefunction for the Ω states, the transition mechanism of the excited states has been accounted for. The transition dipole moments, the Franck-Condon factors, the transition probabilities, and the radiative lifetimes for the transitions have been determined. The calculated lifetimes are much close to the previous experimental and theoretical results. For the phosphorus monohalogen PX(X=Cl, Br, I, At) molecules, the a1Δ state has the longer lifetime than that of the b1Σ+ state.(4) By the data analysis, the successive variation rules of the spectroscopic and transition properties with the atomic structure of the halogen have been derived.