The microwave spectrum of formamide–water and formamide–methanol complexes

Publisher Website
Google Scholar
Abstract
The microwave spectra of the formamide–water and formamide–methanol complexes have been investigated with a pulsed beam Fabry–Perot cavity Fourier transform microwave spectrometer. The observed hyperfine structure due to the 14N nuclear quadrupole interaction was used to assign the rotational transitions for both species. For formamide–water the rotational analysis of ten transitions provides the constants: A=11 227.931(1) MHz, B=4586.9628(10) MHz, C=3258.8278(7) MHz, eQqaa =1.332(3) MHz, and eQqbb =2.037(3) MHz. The formamide–methanol spectrum exhibits an additional splitting from internal rotation of the methyl group. Eighteen observed transitions from the A and E symmetry states have been assigned and fitted with the rotational constants: A=10 186.594(6) MHz, B=2090.36(59) MHz, and C=1762.80(56) MHz with hyperfine constants close to those of formamide–water. By assuming a methyl top moment of inertia Iα =3.206 uÅ2, the barrier to internal rotation V3=231.01(17) cm−1 is obtained. This barrier height is about 36% smaller than that of methanol. The structures determined for these complexes agree well with prior ab initio calculations which indicate essentially planar, double hydrogen bonded structures for both species.