Stark effect molecular beam measurements

The remaining error in the dipole moment Green8 attributes to lack of highly excited configurations. For open-shell molecules it is probable that Hartree-Fock results will be unreliable (see above) and a limited amount of Cl will be essential. Thus even for a Hartree-Fock function the calculated one-electron properties may not agree well with experiment (it should be remembered that, in the most favourable cases where the substance can be studied in a molecular-beam spectrometer and the dipole moment obtained from Stark effect measurements, the experimental error is much less than 0.001 D).28... 

Utilization of both ion and neutral beams for such studies has been reported. Toennies [150] has performed measurements on the inelastic collision cross section for transitions between specified rotational states using a molecular beam apparatus. T1F molecules in the state (J, M) were separated out of a beam traversing an electrostatic four-pole field by virtue of the second-order Stark effect, and were directed into a noble-gas-filled scattering chamber. Molecules which were scattered by less than were then collected in a second four-pole field, and were analyzed for their final rotational state. The beam originated in an effusive oven source and was chopped to obtain a velocity resolution Avjv of about 7 %. The velocity change due to the inelastic encounters was about 0.3 %. Transition probabilities were calculated using time-dependent perturbation theory and the straight-line trajectory approximation. The interaction potential was taken to be purely attractive ... 

Experimental dipole moments can be obtained in several different ways. The first and most widely used approach is based on the measurement of dielectric constants. The second group of methods utilizes microwave spectroscopy and molecular beams (the Stark effect method, the molecular beam method, the electric resonance method, Raman spectroscopy, etc.). 

I Cl isotopomer in the A Hi electronic state employing LIF in a molecular beam. Takei et al. [97Tak] were able to deduce the direction of the molecular electric dipole moment in the A II] state relative to that in theX E ground state by simulating measured Stark effect modulation line shapes. They found both directions to be parallel, in agreement with previous literature results [94Fri, 94Dur]. Thus the polarity in the two states is CF. 

Signs of electric dipole moments, which must be obtained by techniques other than Stark effect measurements, are listed in the column Varia, remarks . There exist some molecular beam deflection data of electric dipole moments which have reached the accuracy of dipole moments determined by microwave spectroscopy or may even be better. These values have been included in columns 3-"6. If there are experimental dipole moments from other spectroscopic regions they are listed too. The methods are given with abbreviations as explained in part 1. 

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