Observation of the J=1 → 2 rotational transition of BaO in a microwave absorption spectrometer at 1700 °C is described. For 135BaO and 137BaO the nuclear electric quadrupole constants, e q0 Q, in the ground vibrational state are reported.
A simple electrostatic polarization model is applied to the low lying electronic states A 2 Π, B 2 ∑+, and A′ 2 Δ of the alkaline earth monohalides which correlate to the electronic d state of the free metal ion. The number of fit parameters can be greatly reduced using relations which are derived from the well known angular part of the free ion wave function. The model predicts energies and electric dipole moments for all Ca, Sr, and Ba monohalides in good agreement with experimental data. The model can also be applied to the C state confirming the highly ionic character of this state.
The spectrum of gaseous KCN was measured in the frequency range between 2 and 39 GHz by microwave absorption and by molecular-beam electric-resonance spectroscopy. Combination of the new results with earlier microwave data of KCN in the 100 GHz range made it possible to assign 64 transitions to the ground vibrational state and to fit them to the asymmetric rotor model. The three rotational constants, the five quartic distortion constants, and two sextic distortion coefficients could be determined. Assuming a CN distance of 1.162(10) Å we find rKC=2.6(1) Å and uKCN=76 °(10). The molecules thus have a nonlinear, T-shaped structure. The inertial defect gives an estimated value of the lowest vibrational frequency of KCN ω2=157 cm−1, which is in reasonable agreement with ω2=139 cm−1 from matrix-isolation studies.
It is shown that the Rittner model is inadequate for the calculation of dipole moments for the alkaline earth monohalides. A modified model is proposed which takes into account explicitly the large charge shifts in the metal ions arising from the polarization. The new model is shown to give results consistent with available experimental data.
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