Low-lying electronic states of the Ti2 dimer: electronic absorption spectroscopy in rare gas matrices in concert with quantum chemical calculations.

Absorption spectra were measured for Ti2 in Ne and Ar matrices. The spectra give evidence for several electronic transitions in the region between 4000 and 10 000 cm(-1) and provide important information about some excited electronic states of Ti2 in proximity to the ground state. The vibrational fine structure measured for these transitions allowed to calculate the force constants and the anharmonicity of the potential energy curves of the excited states, and to estimate changes in the internuclear Ti-Ti distances relative to the electronic ground state. The quantum chemical studies confirm the previously suggested (3)Delta(g) state as the ground state of Ti2. The equilibrium bond distance is calculated to be 195.4 pm. The calculated harmonic frequency of 432 cm(-1) is in good agreement with the experimental value of 407.0 cm(-1). With the aid of the calculations it was possible to assign the experimentally observed transitions in the region between 4000 and 10 000 cm(-1) to the 1 (3)Pi(u)<--(3)Delta(g), 1 (3)Phi(u)<--(3)Delta(g), 2 (3)Pi(u)<--(3)Delta(g), 2 (3)Phi(u)<--(3)Delta(g), and (3)Delta(u)<--(3)Delta(g) excitations (in the order of increasing energy). The calculated relative energies and harmonic frequencies are in pleasing agreement with the experimentally obtained values, with deviations of less than 5% and 2%, respectively. The bond distances estimated on the basis of the experimental spectra tally satisfactorily with the predictions of our calculations.

[Follow-up studies of patients with negative TRH test and normal thyroid hormone levels]. / Verlaufsbeobachtungen bei Patienten mit negativem TRH-Test und normalen Schilddrüsenhormonspiegeln.

The aim of the study was to assess the clinical significance of the association of a negative TRH-test with normal thyroid hormone levels. Therefore, we repeated the investigation in 63 patients one year after the first examination. In 6 patients (10%) hyperthyroidism had developed. Euthyroid autonomy was diagnosed in 11 patients (17%). A prolonged normalisation period of the pituitary-thyroid regulation after having discontinued the thyroid hormone drugs was found in 7 patients (11%). In 40% of the patients the TRH-test remained negative and in 22% of the patients the TSH-response became positive without any known reason. The findings show that a negative TRH-test and normal thyroid hormone levels do not necessarily imply subclinical hyperthyroidism.