Ib Trabjerg

Confirmation of the red band system in MnO4 - as 1T1 ← 1A1 from the effect of pressure on single crystal absorption spectra

The application of uniaxial pressure to single crystals of LiClO4 . 3H2O/LiMnO4. 3H2O and Ba(ClO4)2. 3H2O/Ba(MnO4)2. 3H2O has led to a large splitting of the zerophonon origin line at 13 772 cm-1 in the absorption spectrum of the lithium salt and a much smaller splitting of the 14 247 cm-1 line in the corresponding spectrum of the barium salt. Furthermore, a third line at ∼ 13 764 cm-1 appears in the spectrum of the lithium salt at high pressures. The polarization behaviour of the three lines from the lithium salt is exactly as would be expected for a forbidden electric-dipole 1 T 1 ← 1 A 1 transition in the parent tetrahedral point group.

Temperature dependence of the dual phosphorescence from xanthone in n-hexane matrices

The phosphoresence spectrum and lifetime of xanthone embedded in an n-hexane matrix has been investigated as a function of temperature (1·6-100 K). Vibrational analyses of the spectra reveal that emission occurs from three sites, two of which are dominant. Emission from one site (B) occurs from the 3 nπ* state of a planar xanthone molecule and is characterized by strong totally symmetric carbonyl stretching vibrations and a short lifetime (2·4 ms). Emission from the other site (C) is shown to arise from the 3ππ* state of an out-of-plane distorted xanthone molecule. It displays a vibrational structure rich in modes of a 1, b 1, and b 2 (C 2v notation) symmetry and a long lifetime (115 ms). Both direct spin orbit coupling via configurational mixing of the nπ* and ππ* states due to the non-planarity of the molecule in its 3ππ* state and spin-orbit vibronic interaction involving 3 A 1(ππ*)-1 A 2(nπ*) spin-orbit and 1 A 2(nπ*)-1 B 2(ππ*) vibronic interaction via out-of-plane b 1 vibrations are shown to be resp...

Temperature influence on light absorption by fresh water and seawater in the visible and near-infrared spectrum

The influence of temperature on light transmission in the spectral range from 400 to 760 nm has been determined in a two-cell instrument constructed especially for this purpose. Light transmission was measured over a 1-m path length in both a photometric and a spectral mode in double-ion-exchanged fresh water and filtered seawater with a salinity of approximately 25%?. For both groups of samples the temperature-dependence coefficient of the absorption was found to be -0.00091 ± 0.00006 m(-1) K(-1) in the range from 400 to 550 nm, in contrast to earlier findings. Reproducible signals could be observed only when the samples were left undisturbed for long periods of time between shifts in temperature. The temperature was scanned in alternating directions between 6 and 30 °C in steps of ± 2 °C. The time for recording a set of data was between 2 and 3 weeks. Finally, the temperature dependences of the absorption spectra were recorded in the range 400 to 760 nm. These measurements are only partially in agreement with earlier measurements.

Spectroscopic properties of Cr(CN)63− doped in a KBr crystal

Abstract The ESR, IR, RS electron absorption and emission spectra of Cr(CN) 6 3− trapped in a KBr crystal are studied. The results reveal two different site symmetries of the Cr(III) ion in the host. The effect of the site symmetry on the radiative and non-radiative transition is discussed.

The lowest triplet state of tetramethyl-1,3-cyclobutanedithione. I. Single-crystal polarized absorption spectrum

Abstract The single-crystal polarized absorption spectrum of tetramethyl-1,3-cyclobutanedithione (TMCBDT) has been measured in the region of the lowest triplet state. All bands are polarized exclusively perpendicular to the tetragonal unit cell c axis. The 0-0 band which lies at 594.3 nm is the most intense feature with active vibrations at 309, 329, 600, 913, and 969 cm−1 of lower intensity. The electronic transition is assigned to 3Au ← 1Ag (n∼=) in the D2h molecular point group. Weak, low-frequency vibrations (

The lowest triplet state of tetramethyl-1,3-cyclobutanedithione. III. Single-crystal Zeeman spectroscopy

Abstract Pulsed, high-field Zeeman spectra of the lowest singlet-to-triplet transition in single-crystal tetramethyl-1,3-cyclobutanedithione (TMCBDT) have been measured. The analysis of the spectra was performed using an extension of the theory of Castro and Hochstrasser which allows for an arbitrary alignment of the magnetic field with respect to the principal crystal axes. From this study we provide evidence that in TMCBDT (1) the lowest triplet is 3 A u (D 2h molecular symmetry). (2) only one spin-orbit coupling route is active. (3) a substantial zero-field splitting (2.5 ± 1.0 cm −1 ) is present. (4) the magnetic and molecular axes are rotated by 90°. and (5) the spin-orbit contribution to the triplet-state g values is small compared to its effect on the zero-field splitting parameters.

Luminescence properties of Cr-doped silica sol gel glasses

The emission of Cr-doped silica glass obtained by the sol- gel method is characterized by an orange broad band with a maximum at 610 nm. Its nature is examined by the absorption, excited state absorption, emission, excitation and lifetime measurements over a wide range of temperature and for different concentration of Cr ions. Our measurement show that in spite of fact that the absorption properties of Cr- doped silica sol-gel glass are predominantly associated with Cr4+ centers, the observed in visible range emission can be assigned neither to Cr3+ nor to Cr4+ ions. The discussion of the nature of observed emission was carried out for all possible valencies of the Cr ions. In conclusion is suggested that it may be ascribed to the transitions on the monovalent Cr1+ ion. The reducing agents occurring during the sol-gel process and leading to lowering the Cr valency are discussed.

The 4 A 2→2 E transitions of 2[Cr(en)3Cl3]KCl. 6H2O in strong magnetic fields

The Zeeman effect of the R absorption lines for the pure compound 2[Cr(en)3Cl3]KCl.6H2O has been measured photographically, using a strong pulsed magnet with fields of up to 200 000 gauss at 77 K. The results indicate g ∥ (4 A 2) = 1·82 , g ⊥(4 A 2) = 1·90 with g ∥(Ē) = -1·82 and g ∥ (2Ā) = 1·82. The uncertainties are of the order of ± 0·05.

Trap phosphorescence spectra and lifetimes from crystalline tetramethylcyclobutane-1,3-dithione

Abstract Phosphorescence spectra and lifetimes of single crystal tetramethylcyclobutane-1,3-dithione (TMCBDT) have been measured over the temperature range 1.6–30 K. Analysis of the phosphorescence intensities as a function of temperature shows that the emission originates from a series of defect traps. At low-temperature emission is observed from the individual triplet spin sublevels of a deep-lying trap. The influence of spin-lattice relaxation on the decay from this trap is modelled. Highly selective intersystem crossing into two of the triplet sublevels is shown to occur. First-order spin-orbit coupling of various excited singlets to two sublevels of the emissive 3Au state is suggested as the primary mechanism for S-T intersystem crossing. Evidence is presented that the deepest trap is a thio-dione impurity, probably TMTCBD (tetramethyl-3-thio-1,3-cyclobutanedione).

Magnetic circular dichroism of the first spin-forbidden transition in 2[Cr(en)3Cl3] . KCl . 6H2O

The longitudinal Zeeman effect of the 2 E ←4 A 2 transition of the Cr+3 ion in single crystals of 2[Cr(en)3Cl3] . KCl . 6H2O has been measured using circularly polarized light as a function of magnetic field strength between 0 and 160 kgauss at ∼80 K. The g factor for the ground state was determined to be g ‖(4 A 2) = 2·01±0·05, in agreement with the E.S.R.-determined value. The ratio between the excited state g values and that of the ground state was determined; using the value g ‖(4 A 2) = 1·99, the g factors g ‖(2) = 2·61±0·04 and g ‖() = 1·47±0·04 were obtained.