Electron Microprobe Analysis Of Dental Amalgam

The gas-phase infrared multiple-photon dissociation and detachment (IRMPD) vibrational action spectra of the unsubstituted phenoxide anion and a series of fluorine- and trifluoromethyl-substituted phenoxide anions in the spectral region between 600 and 1800 cm(-1) are presented along with density functional theory (DFT) harmonic vibrational frequency calculations to establish the characteristic vibrations of the phenoxide functionality. The fluorophenoxide anions studied include the conjugate bases of o-, m-, and p-fluorophenol (C6H4FO-) as well as o-, m-, and p-alpha,alpha,alpha-trifluorocresol (CF3C6H4O-). The influence of the substituent on the characteristic vibrational frequencies is interpreted in terms of inductive and resonance shifts. In addition to the dissociation induced by infrared multiple-photon excitation, the electron detachment is also shown to play an important role in the decomposition of the unsubstituted phenoxide. It is demonstrated that the amount of electron detachment relative to dissociation is strongly mitigated by fluorination, and interpretations aided by DFT energy calculations suggest this is primarily due to the increased availability of low-energy dissociation pathways in the substituted phenoxides. Collision-induced dissociation (CID) mass spectrometry of the parent ions is used to estimate relative energies of the dissociation processes, and particular fragmentation motifs are elucidated. In particular, overall HF and CO losses provide facile decomposition pathways, yielding interesting fragment ions such as C6H- or C3H2FO- from the CF3C6H4O- parent anions

Aromatic Excimers: Ab Initio and TD-DFT Study

Excited dimers (excimers) formed by aromatic molecules are important in biological systems as well as in chemical sensing. The structure of many biological systems is governed by excimer formation. Since theoretical studies of such systems provide important information about mutual arrangement of aromatic molecules in structural biology, we carried out extensive calculations on the benzene excimer using EOM-CCSD, RI-CC2, CASPT2, and TD-DFT approaches. For the benzene excimer, we evaluate the reliability of the TD-DFT method based on the B3LYP, PBE, PBE0, and ??PBEh functionals. We extended the calculations to naphthalene, anthracene, and pyrene excimers. We find that nearly parallel stacked forms are the minimum energy structure. On the basis of the benzene to pyrene excimers, we might roughly estimate the equilibrium layer-to-layer distance for bilayer-long arenes in the first singlet excited state, which is predicted to be bound.close7

Non-equilibrium isomer distribution of the gas-phase photoactive yellow protein chromophore

Item does not contain fulltex