Observation and analysis of Fano-like lineshapes in the Raman spectra of molecules adsorbed at metal interfaces

Surface enhanced Raman spectra from molecules (bipyridyl ethylene) adsorbed on gold dumbells are observed to become increasingly asymmetric (Fano-like) at higher incident light intensity. The electronic temperature (inferred from the anti-Stokes (AS) electronic Raman signal increases at the same time while no vibrational AS scattering is seen. These observations are analyzed by assuming that the molecule-metal coupling contains an intensity dependent contribution (resulting from light-induced charge transfer transitions as well as renormalization of the molecule metal tunneling barrier). We find that interference between vibrational and electronic inelastic scattering routes is possible in the presence of strong enough electron-vibrational coupling and can in principle lead to the observed Fano-like feature in the Raman scattering profile. However the best fit to the observed results, including the dependence on incident light intensity and the associated thermal response is obtained from a model that disregards this coupling and accounts for the structure of the continuous electronic component of the Raman scattering signal. The temperatures inferred from the Raman signal are argued to be only of qualitative value.Comment: 20 pages, 12 figure

Electronic Structure and Bonding of Icosahedral Core-Shell Gold-Silver Nanoalloy Clusters Au_(144-x)Ag_x(SR)_60

Atomically precise thiolate-stabilized gold nanoclusters are currently of interest for many cross-disciplinary applications in chemistry, physics and molecular biology. Very recently, synthesis and electronic properties of "nanoalloy" clusters Au_(144-x)Ag_x(SR)_60 were reported. Here, density functional theory is used for electronic structure and bonding in Au_(144-x)Ag_x(SR)_60 based on a structural model of the icosahedral Au_144(SR)_60 that features a 114-atom metal core with 60 symmetry-equivalent surface sites, and a protecting layer of 30 RSAuSR units. In the optimal configuration the 60 surface sites of the core are occupied by silver in Au_84Ag_60(SR)_60. Silver enhances the electron shell structure around the Fermi level in the metal core, which predicts a structured absorption spectrum around the onset (about 0.8 eV) of electronic metal-to-metal transitions. The calculations also imply element-dependent absorption edges for Au(5d) \rightarrow Au(6sp) and Ag(4d) \rightarrow Ag(5sp) interband transitions in the "plasmonic" region, with their relative intensities controlled by the Ag/Au mixing ratio.Comment: 4 figure

Observation and analysis of Fano-like lineshapes in the Raman spectra of molecules adsorbed at metal interfaces

Surface enhanced Raman spectra from molecules (bipyridyl ethylene) adsorbed on gold dumbells are observed to become increasingly asymmetric (Fano-like) at higher incident light intensity. The electronic temperature (inferred from the anti-Stokes (AS) electronic Raman signal increases at the same time while no vibrational AS scattering is seen. These observations are analyzed by assuming that the molecule-metal coupling contains an intensity dependent contribution (resulting from light-induced charge transfer transitions as well as renormalization of the molecule metal tunneling barrier). We find that interference between vibrational and electronic inelastic scattering routes is possible in the presence of strong enough electron-vibrational coupling and can in principle lead to the observed Fano-like feature in the Raman scattering profile. However the best fit to the observed results, including the dependence on incident light intensity and the associated thermal response is obtained from a model that disregards this coupling and accounts for the structure of the continuous electronic component of the Raman scattering signal. The temperatures inferred from the Raman signal are argued to be only of qualitative value

Lifetime use of psychiatric medications and cognition at 43 years of age in schizophrenia in the Northern Finland Birth Cohort 1966

Background: Higher lifetime antipsychotic exposure has been associated with poorer cognition in schizophrenia. The cognitive effects of adjunctive psychiatric medications and lifetime trends of antipsychotic use remain largely unclear. We aimed to study how lifetime and current benzodiazepine and antidepressant medications, lifetime trends of antipsychotic use and antipsychotic polypharmacy are associated with cognitive performance in midlife schizophrenia. Methods: Sixty participants with DSM-IV schizophrenia from the Northern Finland Birth Cohort 1966 were examined at 43 years of age with an extensive cognitive test battery. Cumulative lifetime and current use of psychiatric medications were collected from medical records and interviews. The associations between medication and principal component analysis-based cognitive composite score were analysed using linear regression. Results: Lifetime cumulative DDD years of benzodiazepine and antidepressant medications were not significantly associated with global cognition. Being without antipsychotic medication (for minimum 11 months) before the cognitive examination was associated with better cognitive performance (P = 0.007) and higher lifetime cumulative DDD years of antipsychotics with poorer cognition (P = 0.020), when adjusted for gender, onset age and lifetime hospital treatment days. Other lifetime trends of antipsychotic use, such as a long antipsychotic-free period earlier in the treatment history, and antipsychotic polypharmacy, were not significantly associated with cognition. Conclusions: Based on these naturalistic data, low exposure to adjunctive benzodiazepine and antidepressant medications does not seem to affect cognition nor explain the possible negative effects of high dose long-term antipsychotic medication on cognition in schizophrenia. (C) 2017 Elsevier Masson SAS. All rights reserved.Peer reviewe