Binding Interaction and Raman Spectra of rho-pi Conjugated Molecules Containing CH2/NH2 Groups Adsorbed on Silver Surfaces: A DFT Study of Wagging Modes

作者：Tao, Sha; Yu, Li-Juan; Pang, Ran; Huang, Yi-Fan; Wu, De-Yin^*; Tian, Zhong-Qun

来源：Journal of Physical Chemistry C, 2013, 117(37): 18891-18903.

DOI：10.1021/jp4042777

• INFRARED REFLECTION-ABSORPTION
• EFFECTIVE CORE POTENTIALS
• SERS-ACTIVE SITES
• ADSORPTION STRUCTURES
• AG(110) SURFACES
• VIBRATIONAL FREQUENCIES
• BONDING INTERACTION
• TRANSITION-METALS
• CHARGE-TRANSFER
• ETHYLENE

The wagging mode is a characteristic out-of-plane bending vibration for a series of organic compounds containing -CH2/NH2 groups, such as terminal olefins, p-substituted aniline derivates, and benzyl radicals. The SERS signal of the wagging mode is always sensitive to the interfacial interaction, displaying significant frequency shift and Raman enhancement. To understand the origin of the special SERS signal, density functional theory (DFT) calculation is performed to obtain harmonic vibrational frequencies and Raman intensities of equilibrium structures for the p-pi conjugated molecules adsorbed on silver surfaces on the basis of the molecule metallic cluster model. Our results showed that the frequency shift of the wagging mode is strongly dependent on the hybridization effect, the sp(2) changing to sp(3) hybridization causes a dramatic frequency shift for the wagging mode. Furthermore, our results also revealed the causes of the remarkable enhancement of this mode in SERS intensity. From the point of view of the frontier molecular orbital interaction and the change of electronic structures, the derivatives of polarizability tensor for the wagging coordinate are quite large appearing at the significant extent of the geometry deformation, closely associated with the p-pi conjugation effect and the hybridization property, as well as the energy exchange of the frontier molecular orbitals. The last factor results in significant increases in the derivatives of polarizability tensor along with the direction of the wagging vibrations.

• 出版日期2013-9-19
• 单位厦门大学