W.A.J.A. van der Poel

Complete determination of 14N hyperfine and quadrupole interactions in the metastable triplet state of free‐base porphin via electron spin echo envelope modulation

Through the use of the electron spin echo envelope modulation method, we have accomplished the complete determination of the 14N hyperfine and quadrupole interaction tensors in the lowest photo‐excited triplet state of free‐base porphin in an n‐octane single crystal at ∼1.4 K. The results give insight into the molecular structure of the porphin in the excited state, the relationship between the nitrogen spin density and observed hyperfine couplings, and the effect of hydrogen bonding interactions on the quadrupole coupling constants and principal axes.

Pulsed ENDOR spectroscopy of the interior protons of free-base porphin in its lowest photoexcited triplet state, in an n-octane single crystal

Through the use of the pulsed ENDOR technique, we have obtained the magnetic resonance spectra of the interior protons of free-base porphin in its lowest photoexcited triplet state in a single crystal of n-octane. The values of the components, in the fine structure principal axis system, of the proton-electron hyperfine interaction have been ascertained, and clearly illustrate a departure from D 2h molecular symmetry. The measured tensors have been used to obtain the spin densities at the porphin nitrogen atoms, and the locations of the protons within the ring.

The lowest triplet state of K2Cr2O7. Optical spectra and optically detected electron spin resonance at 1.2 K

Abstract High-resolution emission and excitation spectra are reported for a K2Cr2O7 crystal at 1.2 K, and the effect of microwave saturation on thes

The lowest triplet state of K2Cr2O7. Electron spin resonance in an external magnetic field at 1.2 K

Abstract ESR experiments on the luminescent triplet state of triclinic K 2 Cr 2 O 7 are reported. For the A site D = 24.300, E = 2.324 GHz, for t

The triplet state of the quinoxalinium cation in a quinolinium perchlorate host crystal at 1.2 K

Abstract The prosphorescence spectrum and zero-field transitions are reported for the triplet state of the quinoxalinium cation QH* (singly protonated 1,4-diazanaphthalene) as a guest in quinolinium perchlorate single crystals at 1.2 K. The kinetics of populating and decay of the triplet for QH* in two different sites have been determined by means of the MIDP method. The results do not give support to the idea that the QH* ion is non-planar in its metastable triplet state.

Optically detected proton and nitrogen ENDOR in the 3 Eu state of zinc porphine in an n-octane single crystal

Via optically detected ENDOR the hyperfine tensors of the protons, and partially of the nitrogen atoms, of zinc porphine in its 3 Eu state have been obtained. The results show that the in-plane principal axes of the fine-structure tensor make an angle of 7·8 ± 1·1° with the N-N symmetry axes. The spin densities are evaluated from the hyperfine data in a point-dipole model; a nuclear distortion of b1g symmetry has to be included in order to arrive at a consistent interpretation. The spin densities are compared with calculations and confirm a (eg ← a 2u ) orbital configuration for ZnP in its 3 Eu state.

Characterization of the luminescent triplet state of the K2Cr2O7 crystal and some related systems by EPR and optical spectroscopy at 1.2 K.

Abstract Identification of the lower excited states of the Cr2O2-7 ion. The triplet zero-field splittings and decay prove localization of excitation on one side of the anion in its luminescent state. Preliminary experiments on some further oxo-anions of d0 transition metals likewise extablish the triplet (S = 1) nature of the emitting state (YVO4, CaMoO4, LiVO3, CsVO3).

An EPR Study of the Photoexcited Triplet State of Tetrahedral d° Transition Metal Anions

The excited states of tetrahedral anions which in their groundstate have a d° transition metal at the centre — such as VO4 3-, CrO 4 2-, MnO4 -, and similar compounds with 4d and 5d metals — have since long been the object of study. In an MO description the first excitation corresponds to the “charge-transfer” t1 → 2e, in which the t1 MO’s are linear combinations of 2p AO’s on the oxygens, and the 2e MO’s involve the dx2-y2 and dz2 AO’s on the metal (1). Four electronic states result, the energies of which have been predicted to lie in the order 1T2 > 1T1 > 3T2 ≅ 3T1 (2). In this picture the long-wavelength absorption band of such an ion is the crystal-field-induced 1T1 ← 1A1 transition while the second, much stronger band is the dipole-allowed 1T2 ← 1A1 transition.