MOLECULAR G VALUES, MAGNETIC SUSCEPTIBILITY ANISOTROPIES, AND MOLECULAR QUADRUPOLE MOMENTS IN PROPYNAL

The high-field rotational Zeeman effect has been studied in propynal. The molecular g values are gaa = -0.553 ± 0.002, gbb = -0.040 ± 0.002, and gcc = -0.015 ± 0.001. The magnetic susceptibility anisotropies, in units of 10-6 erg/(G2 mol), are 2χaa - χbb - χcc = 4.4 ± 0.8 and - χaa + 2χbb - χcc = 9.0 ± 1.6. (The a and b axes are in the molecular plane with the angle between the a axis and the near linear C≡C-C link of about 12.6°). Although only the relative signs of the g values are determined experimentally, the above signs are conclusively assigned on the basis of the molecular quadrupole moments. The molecular quadrupole moments, in units of 10-26 esu cm2, are Qaa = 3.1 ± 1.3, Qbb = 1.1 ± 2.2, and Qcc = -4.2 ± 2.4. Using the above g values and magnetic susceptibility anisotropies in conjunction with the known molecular structure, the diagonal elements of the paramagnetic susceptibility tensor and the anisotropies in the second moment of the electronic charge distribution may be calculated. They are χaap = 38.7 ± 0.1, χbbp = 259.3 ± 1.2, and χccp = 270.1 ± 0.8, all in units of 10-6 erg/(G2 mol); and 〈a2〉 - 〈b2〉 = 51.6 ± 0.5, 〈b2〉 - 〈c2〉 = 4.3 ± 0.7, and 〈c2〉 - 〈a2〉 = -55.9 ± 0.4, all in units of 10-16 cm2.