Quantum Chemistry Research On Polycyclic Aromatic Compound

PAHS is a category of important compound.often is found in coal,petroleum asphaltenes,also is considered existing in interstellar medium.PAHs also is kind of circumstance contamination.Some special materials also is associated with PAHs. PAHs research has important meaning in coal conversion. We can design molecule at will when we do quantum chemistry calculation,So we can research conveniencely.Otherwise,we need real PAHs molecule that is absence of. Gaussian 98 ,Gaussian 03 programm are employed to research in this dissertation,based on a lot of calculation,we found that b3lyp/6-31g method is best method consistent with experimental data.Also TDDFT is employed to caculate electronic spectra of some molecules.The caculated data of molecular orbitals make clear the results obtained.Also raman spectra caculated is consistent with experimental data. The results indicate:(1) b3lyp/6-31g method is best method consistent with experimental data.(2)When several PAHs group are connected with alkyl chain and alkyl ring, their p-band electronic spectra are determined by the PAHs whose p-band electronic spectrum is the longest among the PAHs composed of molecule. The cause of this conclusion is that frontier orbital of PAHs is compose of 2pz and 3pz of each conjugated carbon atom,When PAHs group are connected with alkyl chain,only one or two carbon atom near PAHs group contribute to the frontier orbitals of the molecule. (3) When the benzenes of researched molecule with same number of benzenes are arranged along a line, their p-band electronic spectra are longer than the benzenes arranged in a zizag manner. (4)Based on reseach on two categories of PAHs,The result indicate:For the PAHs with same layers of benzene,the polyphenanthrene is more stable than the polyacene.For the polyphenanthrene with different layers of benzene,the molecule with single layer of benzene is more stable than which with double layers,and the molecule with double layers is more stable which with three layers.So is for the polyacene. (5)HOMO,LUMO and the energy gap between of some molecues correlate well with the number of double-bond in the molecule,Also the molecules like biphenyl are researched,indicate electrons of frontier orbital of the molecule move among bridge carbons in different benzene units in a molecule.(6) For the polyphenanthrene and the molecule with phenanthrene like edge,the bond-length that is concave is more longer than which protrudes.(7) The raman spectra of some PAHs molecules is also researched , indicate b3lyp/6-31g method calculate raman spectra correspond to experimental data well. The raman spectra of a category of PAHS like pyrene are very strong.