The rotational spectra for six isotopologues of the complex formed between formamide and formic acid have been measured using a pulsed-beam Fourier transform microwave spectrometer and analyzed to obtain rotational constants and quadrupole coupling parameters. The rotational constants and quadrupole coupling strengths obtained for H C 12OOH- H2 14NCOH are A=5889.465 (2), B=2148.7409 (7), 1575.1234(6), eQq aa =1.014 (5), eQqbb =1.99 (1), and eQqcc =-3.00 (1) MHz. Using the 15 rotational constants obtained for the H 13COOH, HCOOD, DCOOH, and H2 15NCHO isotopologues, key structural parameters were obtained from a least-squares structure fit. Hydrogen bond distances of 1.78 Å for R (O3⋯H) and 1.79 Å for R (H4⋯O1) were obtained. The "best fit" value for the (C-O-H) of formic acid is significantly larger than the monomer value of 106.9° with an optimum value of 121.7(3)°. The complex is nearly planar with inertial defect Δ=-0.158 amu Å2. The formamide proton is moved out of the molecular plane by 15(3)° for the best fit structure. Density functional theory using B3PW91, HCTH407, and TPSS as well as MP2 and CCSD calculations were performed using 6-1++G (d,p) and the results were compared to experimentally determined parameters.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry