Theoretical Investigations On The Potential Energy Surfaces Of The Multi-well Chemical Reactions

Free radical which is an active ingredient of air plays an important role in stabilizing the whole ozonoshphere . Many experimental and theoretical scientists have focused on the gas-phase free radical reactions . In this thesis , the theoretical investigations on two radical reactions , which are HCNO+CN and CH₂ClO₂+ CH₂ClO₂ , have been carried out .Important information of the potential energy surfaces such as the structures and energy of intermediate isomers and transition states, possible reaction channels, reaction mechanisms and major products are obtained. The results obtained in the present thesis may be helpful for further theoretical and experimental studies of this kind of reactions. The main results are summarized as follows:1.The potential energy surface(PES) of HCNO+CN reaction is firstly studied. By analyzing the characteristic of all 11 pathways , it is concluded that the main products of this reaction are NCO+HCN or HCCN+NO rather than HCCN+NO presented by the experimental literature . The possible pathways are listed as follows: Path 1: HCNO+CN→NCC(H)NO→CO+HCNN Path ₂: HCNO+CN→NCC(H)NO→C₂N₂+OH Path 3: HCNO+CN→NCC(H)NO→HCCN+NO Path 4: HCNO+CN→NCC(H)NO→NCO+HCN Path 5: HCNO+CN→NCC(H)NO→HCCO+N₂Path 6: HCNO+CN→NCC(H)NO→N₂+CO+CHIn the experiment Path 3 was considered as the main channel. However, based on our calculated PES the case is different. The energy barrier in the rate-determining step of path 3 is higher than that of the reatants, so it can't be dominant . On the contrary , the energies of all the transition states(TS) and imtermediates (IM) involved in Path 2 and Path 4 are lower than that of the reactants , so both of them are feasible channels . The energy of P4 is the lowest among so many products , so Path 4 is more thermodynamic favorable . Nevertheless , the energy barriers in Path 2 are lower than those in Path 4 which makes Path 2 is more dynamic favorable . Therefore , Path 2 and Path 4 are competitive . More dynamic calculations are needed to determine which path is dominant . The energies of several TS in Path 5 are higher than those of the reactants , so path 5 does not stand strongly in the competition. And P10 which is the secondary product of P5 won't be the main product accordingly. As for other pathways , we have compared their energies of TS in the rate-determining step . We have found E(Path 1)2. .The PES of CH₂ClO₂+ CH₂ClO₂ reaction is firstly studied . According to the experimental paper , there are three channels and all of them will pass an IM which is CH₂ClO₄CH₂Cl . We have found this IM as M1 is formed in the entrance with no TS . All the pathways we have got are listed as follows: Path 1 R→M1→P1(CH₂ClO+O₂) Path 2 R→M1→P2(ClCH₂OOCH₂Cl+O₂) Path 3 R→M1→P3(CH₂ClOH+ClCHO+O₂) Path 4 R→M1→P4(HOOH+ClCHO)It is found out Path 4 , which has not been mentioned in the experiment , is the most favorable channel based on the PES we obtained. Firstly , the energy of P4 is far lower than that of reactants and other products . Secondly , to produce P4 there are no complex steps and no high lying TS , too . Therefore , Path 4 should be the dominant channel . By comparing the energy barriers in the rate-determining step of the other three channels , it can be found that Path 1 is the most favorable , and Path 3 is the second one while Path 2 is the least competitive channel . This conclusion is in line with the experiment .