THE MOLECULAR ELECTRIC QUADRUPOLE TENSOR OF ETHENE FROM THE ROTATIONAL ZEEMAN-EFFECT OF CH2=CD2

The Zeeman effect of several rotational transitions of [1,1-H-2(2)]eth ene has been observed in the millimetre wave range using field strengt hs close to 2.65 T and cell temperatures near - 170 degrees C. The rot ational g values and susceptibility anisotropies fitted to the field s plittings were transferred to those of CH2=CH2 leading to g(aa) = -0.3 954(9), g(bb) = -0.1159(3), g(cc) = 0.0453(2), 2 xi(aa) - xi(bb) - xi( cc) = 0.759(21) x 10(-29) erg G(-2), and 2 xi(bb) - xi(cc) - xi(aa) = 1.926(45) 10(-29) erg G(-2). These data are combined to yield Q(aa) = 1.48(10), Q(bb) = 1.67(19), Q(cc) = -3.16(19) for the principal axis e lectric quadrupole tenser components (all in 10(-26) esu) of ethene. T he errors are standard deviations, and do not include contributions po ssibly arising from zero-point vibrational effects.