Search results for " Spectroscopy"

Hardening in LiF induced by fast Ni ions and recovery of properties under annealing

2005

The recovery of hardness and optical absorbance of LiF crystals irradiated with 640 MeV nickel ions under annealing at 450–810 K is investigated. Recovery of the hardness of irradiated crystals is initiated at temperatures above 530 K, at which a transition from a complex absorption spectrum to a spectrum with only one broad peak at 275 nm is observed. Activation energy of 0.13 eV ± 0.02 eV, which is close to that necessary for migration of H centers, is obtained from the annealing data. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Colour centres in LiBaF3 crystals

1998

Abstract The origin of the absorption bands in LiBaF 3 created by X-ray irradiation at RT has been investigated. It is found that three absorption bands at 270, 320 and 430 nm represent different electron transitions within a radiation defect effectively created in LiBaF 3 single crystals. Following the Mollwo–Ivey relation we discuss investigations of optical dichroism, magnetic optical dichroism, as well as the assumptions regarding the accumulation kinetics of these absorption bands, the F centre being the main radiation defect created by X-rays in undoped LiBaF 3 crystals at RT.

Transient absorption spectra and relaxation kinetics in Nb-doped PbWO4 scintillating crystals

2001

Abstract The spectra and relaxation kinetics of absorption induced by a pulsed electron beam were studied for undoped and Nb-doped PbWO 4 single crystals. A significant influence of Nb doping on transient absorption was found. The influence of Nb doping on the relaxation kinetics is proposed to be due to an oxygen vacancy involving electron–hole recombination. A delay was observed (35– 50 ns ) between the growth of F-centers and the irradiation pulse. A large portion of the F-centers decays within ∼16 μs due to recombination with mobile holes. The prolonged recombination processes are responsible for the decrease of the scintillation yield in PbWO 4 : Nb crystals.

15N NMR studies of tautomerism

2012

The literature related to 15N NMR studies of tautomerism is updated and discussed. The 15N NMR data show that the technique is applicable for both liquid and solid state (both crystalline and amorphous) materials. Modern computational methods combined with experimental NMR data can aid in the chemical shift assignments especially in case of crystalline materials (so-called NMR crystallography). This review article is divided into chapters based on the different classes of compounds and a brief description of experimental and computational NMR techniques is also included.

Mixed spin-state [HS-LS] pairs in a dinuclear spin-transition complex: confirmation by variable-temperature 57Fe Mössbauer spectroscopy.

2008

Exquisite sensitivity of Mossbauer spectroscopy for tiny local molecular distortion is demonstrated in [FeII2(pmat)2](BF4)4?DMF: high-spin (HS) iron(II) in [HS-HS] and in [LS-HS] (low-spin–high-spin) pairs is clearly distinguished (see picture) for the first time without the need to apply a magnetic field. This dinuclear complex clearly shows that spin crossover via a [LS-HS] species is promoted by the use of a highly constrained bridging ligand (the bis-terdentate pmat).

Spectroscopic Investigation of the System TeCl4/[NEt4]PF6 in Solution and the Crystal Structure of [NEt4]2[Te2Cl10].

2005

Solutions containing TeCl 4 and [NEt 4 ][PF 6 ] in CH 2 Cl 2 were investigated by means of UV/vis and NMR spectroscopy in order to study the complex chemistry of TeCl 4 with the [PF 6 ] - anion. The results show formation of [TeCl 5 ] - and strong interactions of [PF 6 ] - with a tellurium containing species, presumably [TeCl 3 ] + . The life time of the Te I V -PF 6 complex is long enough to give different signals in the 1 9 F NMR spectrum of a solution containing excess [PF 6 ] - . Even a fivefold excess of Cl - ions over [PF 6 ] - does hardly lead to a dissociation of [TeCl 3 ...PF 6 ]. Crystals of [NEt 4 ] 2 [Te 2 Cl 1 0 ] were obtained from a 4:1 solution of [NEt 4 ]PF 6 and TeCl 4 in …

Photoelectron spectrum of poly(methyl-n-propylsilane): a valence band theoretical interpretation

1996

Abstract The results of a theoretical investigation of the photoelectron spectrum of poly(methyl-n-propylsilane) are reported. The simulation of the UPS spectrum has been obtained from band structure calculations performed using the valence effective Hamiltonian method (VEH). The theoretical spectrum is fully consistent with the experimental UPS spectrum, and an excellent quantitative agreement is observed when the energies of the main peaks of both spectra are compared. A complete analysis of the contributions to the main peaks, together with a detailed interpretation of all the photoemission bands observed in the experimental spectrum have also been performed.

Unprecedented Hexa- and Undecanuclear Frameworks of Two New Tin(IV) Oxo Clusters Resulting from Partial Debenzylation Reactions

2010

A new and facile synthetic route to the known neutral cluster ((PhCH2)2SnO)6[((PhCH2)2SnOH)2- (CO3)]2 (2) as well as its reactivity toward trifluoromethanesulfonic acid (HO3SCF3, TfOH) are reported. The solid-state structure of the new solvate 2·6C7H8 has been determined by single-crystal X-ray diffraction. The core of 2 can be described as a pair of coplanar pentanuclear [(PhCH2)2SnO]5 ladders bridged at their ends by two carbonate groups. Successive additions of TfOH to a suspension of 2 in CD3CN were monitored by 119Sn{1H} NMR spectroscopy showing the transformation of the fingerprint of 2 (δ = −244, −246, −306 ppm), via new upfield signals, to a final broad resonance located at δ = −474…

Vibrational spectroscopy of a tetraureidocalix[4]arene based molecular capsuleElectronic supplementary information (ESI) available: three tables cont…

2001

Structural models for self-assembled dimers composed of two urea calix[4]arenes which entrap benzene or cyclohexane are developed using Fourier transform infrared (FTIR) spectroscopy. Based on the host–guest ratio determined by 1H NMR spectroscopy in solution, and confirmed for the solid state by a thermogravimetric analysis, it is possible to prove by a comparison of the FTIR data of host, guest, complex and model compounds, that the capsule is held together by a cyclic array of weak and strong hydrogen bonds between the urea units attached at the wide rim of the calixarenes. The dimerization of the two urea units leads to a loss of symmetry, and an averaged C4 symmetrical arrangement is p…

1977

Solutions of chain- (PS-d3) and phenyl ring (PS-d5) deuterated polystyrenes in perdeuterated PS-d8 have been investigated with 1H and 2D NMR relaxation and wide line methods. The intra- and intermolecular parts of the 1H second moments at −100°C are 3,7 G2 and 2,0 G2, respectively, for PS-d3, and 14,7 G2 and ca. 0 G2, respectively, for PS-d5. The intermolecular contribution to the 1H spin lattice relaxation rate, determined at 55 MHz between 150°C and 250°C, is about one third of the total rate in PS-d3, and negligible in PS-d5. We suggest that this contribution is caused by rotational fluctuations of the intermolecular H H vectors. The intramolecular 1H- and 2D-relaxation rates indicate th…