Theoretical Studies On The Excited States Of Several Important Small Molecular Pollutants In Atmosphere

The samll molecules including sulphur have received much attention asthe important pollutants in the atmosphere. These molecules particates inmany photo-chemical and photo-physical reactions and produce thehydrogen sulfide and the oxygen sulfides, which are can destroy the ozone.For example the HSO can destroy the ozone through the following cycle:HS+O₃→HSO+O₂, and HSO+O₃→HS+2O₂. In this thesis theCASPT2/CASSCF calculations are perfomed to investigate four importantsulfide molecules. The geometries, energies and the frequencies areresearched. The main results are summarized as followed.1. At CASPT2/CASSCF by using ANO-L basis set we researched the HSOand HSO+ molecules. The equilibrium geometries, energies and thevibration freqencies of several electronic states are obained. The alterationof the geometries between the excited states and the ground state areexplained very well based on the electronic structures. Thhrough the verticalcalculations we calculated the valence exciteds tates and the rydberg excitedstates. In vertical calculations we used ANO-L+ basis set, which are obtainedfrom the ANO-L basis set augmented with a set of s, p, d functions. The ground state of the HSO molecule is comfirmed as the 12A″. Itselectronic structure is (core)(6a')²(7a')²(8a')²(9a')²(2a")²(10a')²(3a")¹. Theground state of the HSO+ molecule is 12A′ state, which can be describedthrough removing the single electron of the HSO radical. In a wide rangebetween 9.79¹8.90eV total fifteen ionic states are confirmed, in which nineelectronic states are located adiabatically. Through the comparison betweenthe vertical and the adiabatic results we predict three sharp peaks at 9.77,10.85 and 11.49eV, respectively. at the some time we also calculated eightvalence exciteds tates below 10.35eV, which are 12A′,22A′,22A″,32A′,32A″,42A″ and 42A′. these states correspond to the adiabatic ionizationenergies 2.50,4.46,4.66,5.46,6.02,6.14 and 6.16eV. The other eightelectronic state are 52A′,52A″,62A′,62A″,72A′,72A″,82A″and 92A″,which can be described with the transitions from the HOMO to the rydbergorbital 3s,3pz,3py,3dyz,3px,3dxz,4pz and 5pz and has the excited energies6.84,7.35,7.59,7.99,8.10,8.75,9.95 and 10.35eV, respectively. Throughthe vibration frequencies analyses we can confirm the geometries calculatedby us are the stationary points in energy surfaces.2. At CASPT2/CASSCF by using ANO-L basis set we researched the HO2and HO2+ molecules. The structural parameters, energies and the vibrationfrequencies are analyzed in detail. We use the ANO-L basis set in theoptimization process and the ANO-L+ basis set (ANO-L augmented with aset of s, p, d functions) through the vertical calculations.For the HO2 radical we confirm the ground state as the 12A″ state,which's electronic structure is (core)(5a′)2(6a′)2(1a″)2(7a′)2(2a″)1. The othertwo optimized electronic states are 12A′ and 22A″, which correspond to thesingle transtions 7a′→2a″(n→π*) and 1a″→2a″(π→π*), respectively. Thetransition energies are 0.921 and 4.158eV more consistent consistent withthe former experimental data than the former theoretical calculations. Wecorrect the former assignment to the first and the second electronic states.The vibration frequencies analyses prove these electronic states as thestationary points in energy surfaces.3. At CASPT2/CASSCF by using gauss type basis set 6-311++G(3df, 3pd)we researched the CH3S, CH3S+ and CH3S-molecules. The structures,energies, the vibration frequencies and the absorption spectrum arecalculated. The ionization and the affinity energies in adiabatic and verticalcalculations are discussed.We optimized the geometries of six electronic states of the CH3Sradical in Cs point group and performed the single point energy correction atCASPT2 level. The ground state of the radical is 12A′. The first excited stateis 12A″, which is 0.078eV higher than the ground state. This value isconsistent with the experimental value. The Jahn-Teller effect is provedaffect this molecule slightly and the radical keeps in C3v point groupessentially. The ground state 12A′ and the excited state 12A″ are two parts inCs point group of the 2E geometry in C3v point group. The geometricaldistortion are explained well based on the electronic structures.For the CH3S+ cation we optimized ten electronic states at CASSCFlevel in Cs point group. The ground state is 13A″, in which the singleelectrons lying in one a′ and one a″ orbital. Through the comparisonbetween the ground state of the radical and the ionic states of the cation weobtained the ionization energies 9.31,10.13,10.28,11.41,12.23,12.48,12.83,14.27,14.35 and 14.42eV in an energy increasing order. These statescorrespond to the ionic states 13A″, 11A″, 11A′, 21A′, 13A′, 23A″, 21A″, 33A″,23A′ and 33A′, respectively. For the CH3S-cation we optimized sevenelectronic states at CASSCF level in Cs point group. Through the energycomparison between the anion and the radical we obtained the electronaffinity energies.4. At CASPT2/CASSCF by using gauss type basis set 6-311++G(3df, 3pd)we researched the CH3CH2S, CH3CH2S+ and CH3CH2S-molecules. Weresearch the structures, energies and the vibration frequencies of these threemolecules.For the radical the ground state is 12A″ and the electronic structure is(core)(2a″)2 (10a′)2(11a′)2(3a″)2(12a′)2(13a′)2(4a″)1. through the calculationfor three excited states 22A″, 12A′ and 22A′, we found that the most severegeometrical distortion happens in 22A′ and is explained with the electrontransitions. For the CH3CH2S+ cation the ground state is 13A″ and theelectronic structures is (core)(2a″)2(10a′)2(11a′)2(3a″)2(12a′)2(13a′)1 (4a″)1.For the CH3CH2S-anion the ground state is 11A′ and the electronic structureis (core)(2a″)2(10a′)2(11a′)2(3a″)2(12a′)2(13a′)2(4a″)2. All of the geometricaldistortions are explained very well with the electronic transitions.