Methyl Nitrate, its Molecular Values, Magnetic Susceptibility Anisotropies, Molecular Electric Quadrupole Moment, Second Moments of the Electronic Charge Distribution, and Electric Field Gradient at the Nitrogen Nucleus

Abstract

The high field molecular Zeeman effect of low-J rotational transitions has been observed in methyl nitrate. The spectrum is complicated by the presence of the small 14N nuclear quadrupole coupling. Methyl top internal rotating splitting is negligible in the transitions studied here. From line shape analyses the individual satellite frequencies in the Zeeman-hfs-multiplets could be determined with experimental uncertainties typically smaller than ±2 kHz. The molecular Zeeman parameters and the 14N nitrogen coupling constants were fitted simultaneously to the observed splittings. The molecular g-values are gaa = -0.1168(5), gbb= -0.0449(3), and gcc= -0.0235(4). The molecular magnetic susceptibility anisotropies in units of 10-6 erg gauss-2 mol-1 are 2ξaa -ξbb -ξcc = +1.24(54) and 2ξbb - ξcc - ξaa = +13.14(53). The 14N nuclear quadrupole coupling constants are χaa - + 0.308(17) MHz, χbb - χcc -0.262(31) MHz. The molecular electric quadrupole moments calculated from the observed rotational constants and Zeeman parameters in units of 10-26 esu cm2 are Qaa = +3.4(6), Qbb= -4.6(6), and Qcc= +1.2(10). Knowledge of the molecular structure and the molecular g-values also gives the diagonal elements in the paramagnetic susceptibility tensor and the ansiotropies in the second moments of the electronic charge distribution. The results in units of 10-6 era gauss-2 mole-1 are ξp aa = + 118.14(10), ξp bb = +279.73(14), and ξp cc = + 357.40(26), and ⟨a2⟩ - ⟨b2⟩ = + 37.14(14) Å2, ⟨b2⟩ - ⟨c2⟩ = +20.46(22) Å2, and ⟨c2⟩ -⟨a2⟩ = -57.60(21) Å2