Search results for "molecule"

Electron impact mass spectra of chlorinated methyl propanoates

1982

The mass spectral fragmentations of all eleven chlorinated methyl propanoates have been studied. Deuterium labelling and metastable ion analysis were used to elucidate the fragmentation mechanism. The molecular ion peaks of all compounds are small, except methyl 3,3-dichloropanoate (38%). In most cases α-cleavage gives the base peak [COOCH3]+, and the loss of a chlorine atom from the molecular ion is characteristic of the 3-chloro, 3,3-dichloro and 3,3,3-trichloro compounds. Metastable ions showed the losses of small neutral molecules such as CH3OH, CH2CO, CO2 and CO from the [MCl]+ ion. α-Cleavage and the loss of Cl˙ gives an intense [MCOOCH3Cl]+˙ peak, which is the base peak in the spectr…

Donor-acceptor substituted polyenes : orientation in mono- and multilayers

1992

Large molecules containing different chemical units whose interactions within the molecule result in new macroscopically observable effects, have become increasingly important.The organization of molecules of this type in ordered structures leads to functional molecular materials.Their use in molecular electronics requires that the units exhibit specific electronic properties. Recently, we reported on the intramolecular energy transfer through terminally substituted conjugated polyenes. An intramolecular electron transfer within donor-acceptor substituted polyenes can be achieved by introducing suitable terminal groups.

Die darstellung höhermolekularer polymer- und molekular-einheitlicher phenol-formaldehydkondensate

1956

Es werden molekulareinheitliche Phenol-Formaldehydkondensate bis zu einem Molekulargewicht von 1400 dargestellt. Phenol-formaldehyde-condensates are prepared, which have molecules with uniform molecular weight; the maximally obtained height is 1400.

Enhanced porosity in a new 3D Hofmann-like network exhibiting humidity sensitive cooperative spin transitions at room temperature

2011

The porous coordination polymers (PCPs) of general formula {Fe(bpac)[M(CN)4]}·guest (M = Pt, Pd) exhibit larger channels than previously synthesised 3D-Hofmann-like PCP. The channels are partially occupied by uncoordinated guest bpac ligands and labile H2O molecules. These PCPs exhibit very scarce cooperative spin crossover behaviour around room temperature with a large hysteresis loop (up to 49 K) and also display sensitivity to humidity and guest molecules. The inclusion of bpac molecules in the 3D network can be avoided by adding competitive volatile molecules during the crystallization process, affording the guest-free material. The spin crossover behavior of different guest and guest-f…

Thermal effects on small para-hydrogen clusters

2010

A brief review of different quantum Monte Carlo simulations of small (p-H2)N clusters is presented. The clusters are viewed as a set of N structureless p-H2 molecules, interacting via an isotropic pairwise potential. Properties as superfluidity, magic numbers, radial structure, excitation spectra, and abundance production of (p-H2)N clusters are discussed and, whenever possible, a comparison with 4HeN droplets is presented. All together, the simulations indicate that temperature has a paradoxical effect of the properties of (p-H2)N clusters, as they are solid-like at high T and liquid-like at low T, due to quantum delocalization at the lowest temperature. © 2010 Wiley Periodicals, Inc. Int …

A Discussion of Some Problems Associated with the Quantum Mechanical Treatment of Open-Shell Molecules

2003

Consequences of the One-Electron Reduction and Photoexcitation of Unsymmetric Bis-imidazolium Salts

2012

Coupling of uronium salts with in situ generated N-heterocyclic carbenes provides straightforward access to symmetrical [4](2+) and unsymmetrical bis-imidazolium salts [6](2+) and [9](2+) . As indicated by cyclic and square-wave voltammetry, [6](2+) and [9](2+) can be (irreversibly) reduced by one electron. The initially formed radicals [6](.+) and [9](.+) undergo further reactions, which were probed by EPR spectroscopy and density functional calculations. The final products of the two-electron reduction are the two carbenes. Upon irradiation with UV light both [6](2+) and [9](2+) emit at room temperature in solution but with dramatically different characteristics. The different fluorescenc…

Diffusion and reactions of interstitial oxygen species in amorphous SiO2: A review

2008

This article briefly summarizes the diffusion and reactions of interstitial oxygen species in amorphous SiO 2 (a-SiO 2 ). The most common form of interstitial oxygen species is oxygen molecule (O 2 ), which is sensitively detectable via its characteristic infrared photoluminescence (PL) at 1272 nm. The PL observation of interstitial 0 2 provides key data to verify various processes related to interstitial oxygen species: the dominant role of interstitial O 2 in long-range oxygen transport in a-SiO 2 ; formation of the Frenkel defect pair (Si-Si bond and interstitial oxygen atom, 0°) by dense electronic excitation; efficient photolysis of interstitial O 2 into O° with F 2 laser light (λ= 157…

A Diferrous Single‐Molecule Magnet

2007

The diferrous complex [Fe2(acpypentO)(NCO)3] (1),(acpypentO– = the anion of 1,5-bis[2-pyridyl(1-ethylimino)]pentane-3-ol) was studied by spectroscopic (dual-mode X-band EPR and 57Fe-Mossbauer) and magnetic (AC magnetic susceptibility) techniques. Complex 1 (A. K. Boudalis et al., Inorg. Chem.2004, 43, 1574) was previously shown to exhibit an intramolecular ferromagnetic coupling with important single-ion anisotropies with marked differences in the single-ion electronic parameters of the two iron sites. In this contribution, additional studies are carried out to probe its dynamic magnetic properties. Mossbauer spectra recorded at liquid helium temperatures indicate slow paramagnetic relaxati…

Relaxation Mechanisms of 5-Azacytosine.

2015

The photophysics and deactivation pathways of the noncanonical 5-azacytosine nucleobase were studied using the CASPT2//CASSCF protocol. One of the most significant differences with respect to the parent molecule cytosine is the presence of a dark (1)(nNπ*) excited state placed energetically below the bright excited state (1)(ππ*) at the Franck-Condon region. The main photoresponse of the system is a presumably efficient radiationless decay back to the original ground state, mediated by two accessible conical intersections involving a population transfer from the (1)(ππ*) and the (1)(nNπ*) states to the ground state. Therefore, a minor contribution of the triplet states in the photophysics o…