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Dielectric constants have been determined for dimethylsiloxane chains (CH3)3Si[OSi(CHJ210Si(CH3)3 in the thermodynamically good solvent cyclohexane and in the undiluted state, for degrees of polymerization x + 1 ranging from lQ2 to 1/nm 2 (where <,...2> is the mean-square dipole moment of a chain consisting of n = 2x + 2 bond dipoles of magnitude m) is independent of chain length, as has been predicted for chains of such structural symmetry. Unfortunately, comparison of the experimental values of the dipole moment ratio with those predicted from rotational isomeric state theory is complicated by pronounced specific solvent effects and comparison of experimental and theoretical values of d In<,...2>/dT is also difficult because of the very small magnitUde of this coefficient.

The dipole moments of a series of charge-transfer complexes of methylbenzenes with tetracyanoethylene in carbon tetrachloride solutions at 25 "C and the various parameters derived from Mulliken's theory have been evaluated. The energies of various states of the complexes were calculated via their relationships with the parameters, charge-transfer transition energies, and heats of formation of the complexes by means of the variation principle. Vertical ionization potentials of the donors were obtained from the calculated energies of the dative structures of the complexes. The dipole moments contributed from the charge-transfer interaction can also be reasonably interpreted as charge-transfer energies in terms of vertical ionization potentials of the donors.

Vibration–rotational spectra of 205Tl19F and 203Tl19F in the electronic ground state X0+ were measured in absorption in the range of wave number [Formula: see text] with diode lasers as spectral sources. Analysis of all available data yielded values of coefficients of radial functions for the potential energy and other molecular properties; only eight independently fitted and two constrained parameters sufficed to reproduce satisfactorily and with physical meaning the frequencies and wave numbers of about 890 distinct pure rotational and vibration–rotational transitions. Independent of nuclear mass, the equilibrium internuclear separation Re of TlF is (2.084 3517 ± 0.000 0039) × 10−10 m; the maximum range of validity of radial functions is 1.85 ≤ R/10−10 m ≤ 2.45. Comparing these results with those of InF, we attribute the large magnitude of [Formula: see text] to the finite and isotopically varying nuclear volume of Tl rather than to (adiabatic) effects of nuclear mass, whereas no such effect is detectable for In in InF. Other aspects of nonadiabatic effects for these polar molecules TlF and InF are discussed.

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