MOLECULAR G-VALUES MAGNETIC SUSCEPTIBILITY ANISOTROPIES SECOND MOMENT OF CHARGE DISTRIBUTION AND MOLECULAR QUADRUPOLE MOMENTS IN FORMIC ACID

The high-field rotational Zeeman effect has been observed in formic acid. The molecular g values and anisotropics in the magnetic susceptibilities are gaa = –0.2797 ± 0.006, gbb = –0.0903 ± 0.0006, gcc= -0.0270 ± 0.0006, 2χaa -χbb - χcc = (3.4 ± 0.5) x 10-6 erg/(G2 mole), and 2χbb - χaa - χcc = (9.4 ± 0.3) X 10-6 erg/(G2 mole). Only the relative signs of the g values are determined experimentally. However, by comparing the calculated molecular quadrupole moments (for both all positive and all negative g values) with known values for other similar molecules, the above negative signs are conclusively assigned. The molecular quadrupole moments are Qαα = -(5.3 ± 0.4) x 10-26 esu cm2, Qbb = +(5.2 ± 0.4) x 10-26esu cm2, and Qcc = +(0.1 ± 0.4) x 10-26 esu cm2. The a axis is nearly along a line connecting the two oxygen atoms, and this axis makes an angle of 31.6° with the C=0 bond direction. The b axis is also in the OCO plane. The diagonal elements in the total magnetic susceptibility tensor are χaa = -(18.8 ± 0.8) x 10-6 erg/(G2 mole), χbb = -(16.8 ±0.8) x 10-6 erg/(G2 mole), and χcc = –(24.2 ± 0.8) x 10-6 erg/(G2 mole). The diagonal elements in the paramagnetic susceptibility tensor are Xααp = (28.8 ± 0.1) x 10-6, Xpp = (106.5 ± 0.1) x 10-6, and Xccp = (117.2 ± 0.1) x 10- 6 all in units of erg/(G2 mole). The diagonal elements in the second moment of the electronic charge distribution are 〈2〉 = (26.6 ± 0.3) x 10-16cm2, 〈2〉 = (7.7 ± 0.3) x 10-16 cm2, and〈c2〉 = (3.5 ± 0.2) x 10-16 cm2. © 1969, American Chemical Society. All rights reserved.