Near- and Deep-Ultraviolet Resonance Raman Spectroscopy of Pyrazine-Al4 Complex and Al3-Pyrazine-Al3 Junction

摘要

Near- and deep-ultraviolet (UV) resonance Raman spectroscopy of pyrazine-Al4 complex and Al3-pyrazine-Al3 junction was investigated theoretically with a quantum chemical method. Here, 325 and 244 nm were employed as near- and deep-UV sources in our theoretical study. The intensities of static normal Raman spectra of pyrazine-Al4 complex and Al3-pyrazine-Al3 junction were enhanced on the orders of 10 and 10~3 by a static chemical mechanism, respectively. The calculated absorption spectra reveal strong ~6B2 and ~(13)B_(2u) electronic transitions near 325 nm for pyrazine-Al4 complex and 244 nm for Al3-pyrazine-Al3 junction, respectively. The analyses of orbital transitions in electronic transitions reveal they are the mixture of (metal to molecule) charge transfer excitation and intracluster excitation. The intensity of near-UV resonance Raman spectroscopy of pyrazine-Al4 complex and the intensity of deep-UV resonance Raman spectroscopy of Al3-pyrazine-Al3 junction are strongly enhanced on the order of 10~5 and 10~4, respectively, compared to the Raman intensity of isolated pyrazine excited at 325 and 244 nm. The calculations of Mie theory and the three-dimensional finite-difference time domain method reveal strong surface plasmon resonance and strong electromagnetic enhancements at 325 and 244 nm for single and dimer nanoparticles at suitable sizes and gap distance, respectively. The strongest SERS enhancement in the system of junction is on the order of 10~8 at the incident lights of 325 and 244 nm. The total enhancements, including the chemical and electromagnetic enhancements, can reach up to 10~(13). So, Al is a suitable material for near- and deep-UV surface-enhanced resonance Raman scattering.