Theoretical Studies On Photodissociation Dynamics Of Water And Thiophenol Molecules

Photodissociation is the most fundamental process in photochemistry,which is the typical reactions in atmosphere chemistry,interstellar chemistry,combustion chemistry and environmental chemistry et al.It is an ideal system to study the excited dynamics,multidimensional dynamics,tunneling,conical intersection,non-Born-Oppenheimer dynamics,reaction selectivity and specificity,and so on.In the last few decades,tremendous progress had been made both in experimental and theoretical researches.The rapid development in experiment technique and computational capabilities motivate the photodissociation to move to areas with higher resolution,more meticulous and intrinsical.But it is still challenging to construct potential energy surfaces for larger,complex systems and develop new dynamics theory for higher-dimensional molecular systems with coupling of angular momentum and non-adiabatic effects.The photodissociation of the water molecule is an excellent paradigm in polyatomic molecular photodissociation dynamics.It also plays important roles in exploring the chemical evolution in the universe,making use of water resources and environmental protection et al.Based on the high accuracy potential energy surfaces of water constructed by our groups,we explored the dynamics of deuterated water at first.We constructed a two-dimensional Hamiltonian considering the conical intersection of ground state Xand second excited state B.The Chebyshev real wavepacket method was used to propagate the wavepacket.It was found that the non-adiabatic channel was the major and more OD(X)products were achieved.The dissociation was direct and quick.It made the products mainly in vibrational ground state with higher rotationally excited.OD(A)products were formed through the adiabatic channel showing property of some long-lived resonance states,which made it more complex.By the way,the absorption spectrum,branching ratios,vibrational and rotational distributions of OD products were all in reasonably agreement with the latest experimental results.With the same model,we investigated the state-to-state photodissociation dynamics of vibrationally excited water in the B band.As the different vibrational states had different wavefunctions,different spectrum,branching ratios and product distributions were gained.Among those differences,the bend vibrational excited state showed the most interesting results.It gave a two lobes structure with a shallow minimum on the absorption spectrum,and a dominant vibrational inverted population OH(X,v = 1)fragment at higher energy was generated which confirmed a nearly single rotational product propensity.The bond-stretching vibrational states(0,0,1)and(1,0,0)showed high X/A branching ratios at short photon wavelength,which indicated that dissociation proceeded can mainly via the adiabatic channel at some specific vibrationally excited.Aromatic compounds are important parts of organic chemistry,biologic chemistry and food chemistry et al.The basic structure of elementary amino acids constituting human proteins like Histidine,Tryptophan,Leucine and the all base constituting DNA and RNA are five or sixed membered aromatic rings.In the last tens of years,chromophores in biological systems as phenol,imidazole and pyrrole had attracted enormous attentions of experimental and theoretical researchers majored in photochemistry.Firstly in experiment,it was found that these molecules had strong UV-vis absorbance,but gave low efficiency to radiate.It must be accounted for a fast nonradiative energy decay process.And it took effect for protecting human with light absorbance.We were the first to construct a three-dimensional potential energy surfaces of thiophenol.We performed a three-dimensional dynamics study with the diabatic potential energy surfaces then and had deeper understand of the non-adiabatic photodissociation procedure of thiophenol.We carried out the electronic structure calculations with the explicitly correlated multireference configuration interaction(MRCI-F12)method and the cc-pVTZ-F 12 basis,which considering the dynamic electronic correlation more sufficiently.Then we used the linear-vibronic coupling model to calculate the non-adiabatic coupling and finally got a three-dimensional non-adiabatic potential energy surface containing the S-H stretch,C-S-H bend and C-C-S-H torsion.We calculated the vibrational energy levels of PhSH and PhSD both for S0 and S1 states.It had a good agreement with the available experiment data.We also propagated the wavepacket with second-order split operator method.It clearly showed a fast non-adiabatic dissociation reaction.The branching ratios achieved were also qualitatively comparable with the experiment work.Besides,we used the Chebyshev method to propagate the wavepacket and obtained a complex energy of the resonance,then getting the lifetime of vibronic states on S1 with low-storage filter diagonalization method.It also gave a fast photodissociation reaction and the lifetime were at the magnitude of scores of fs.At last,we discussed the geometric phase effect in thiophenol dynamics.The adiabatic treatment without geometric phase yielded lifetimes two orders of magnitude shorter than the exact ones.Compared with phenol,less difference was made.The main reason was the barrier to overcome for thiophenol is much lower than phenol.The second reason was the wavefunction distributed both side of zero torsional angle,and the destructive interference on the ??*state was not such strong as phenol.This two reasons together made the less distinct.However,the difference in wavefunction was prominent.It was because of the antisymmetry of diabatic coupling with torsional angle equal to zero thus leading the destructive interference.But in adiabatic model,it could never be reached.We confirmed that geometric phase must be included in the dynamics model then a correct results would be obtained.And these results can establish a substantial foundation for the future study.