中文摘要：

采用共振拉曼光谱技术和密度泛函理论方法研究了6-N,N-二甲基腺嘌呤（DMA）的A带和B带电子激发和Franck-Condon区域结构动力学.πH→πL＊跃迁是A带吸收的主体,其振子强度约占整个A带吸收的79%.由弥散轨道参与的n→Ryd和πH→Ryd跃迁在B带跃迁中扮演重要角色,其振子强度约占B带吸收的62%,而在A带吸收中占主导的πH→πL＊跃迁的振子强度在B带吸收中仅占33%.嘌呤环变形伸缩＋C8H/N9H面内弯曲振动ν23和五元环变形伸缩＋C8H弯曲振动ν13的基频、泛频和合频占据了A带共振拉曼光谱强度的绝大部分,说明1πHπL＊激发态结构动力学主要沿嘌呤环的变形伸缩振动,N9H/C8H/C2H弯曲振动等反应坐标展开,而ν10,ν29,ν21,ν26和ν40的基频、泛频和合频占据了B带共振拉曼光谱强度的主体部分,它们决定了B带激发态的结构动力学.A带共振拉曼光谱中ν26和ν12被认为与1nπ＊/1ππ＊势能面锥型交叉有关.B带共振拉曼光谱中ν21的激活与1ππ＊/1πσ＊N9H势能面锥型交叉相关.

英文摘要：

The A-and B-band electronic excitations and the excited state structural dynamics of 6-N,N-dimethyladenine（DMA） were studied by resonance Raman spectroscopy and density functional theory calculations.The πH→πL＊ transition is the main part of the A-band absorption and its calculated oscillator strength occupies 79% of the A-band absorption.n→Ryd and πH→Ryd transitions where Ryd denotes the diffuse Rydberg orbital play important roles in the B-band electronic transitions and their calculated oscillator strengths occupy about 62% of the B-band absorption.The oscillator strength for the πH→πL＊ transition,which dominates the A-band electronic transition only occupies about 33% of the B-band absorption.The foundamental vibrations of the purine ring deformation stretch plus the C8H/N9H bend mode ν23 and the 5 member ring deformation stretch plus the C8H bend mode ν13,and their overtones and combination bands occupy most of the A-band resonance Raman intensities.Therefore,the 1πHπL＊ excited state structural dynamics of DMA is mainly along the ν23 and ν13 reaction coordinates.The majority of the B-band resonance Raman intensities are dominated by the fundamental vibrations of ν10,ν29,ν21,ν26,ν40,and their overtones and combination bands.This suggests the B-band excited state structural dynamics of DMA is mostly along the purine ring deformation,the C6N10 stretch,the N9H/C8H/C2H bend and the N（CH3）2 antisymmetric stretch.The appearance of ν26 and ν12 in the A-band resonance Raman spectrum is correlated to the Franck-Condon region 1nπ＊/1ππ＊ conical intersection.The activation of ν21 in the B-band resonance Raman spectrum is correlated to the Franck-Condon region 1ππ＊/1πσ＊N9H conical intersection.