The torsional–rotational spectrum and structure of the formaldehyde dimer

Publisher Website
Google Scholar
Abstract
The microwave spectra of (H2CO)2 and (D2CO)2 have been observed with a pulsed beam, Fabry–Perot cavity, Fourier transform microwave spectrometer. Both species exhibit a-type spectra which are split by internal rotation of each monomer unit and an interchange of donor–acceptor bonding roles analogous to the water dimer. Rotational analysis of each spectrum provides the constants A=18583.(54) MHz, 1/2 (B+C)=3272.105(34) MHz, and B−C=503.92(17) MHz for (H2 CO)2 and A=14 862.1(35) MHz, 1/2 (B+C)=3030.2366(37) MHz, and B−C=490.977(18) MHz for (D2CO)2. Stark effect measurements result in derived electric dipole components μa =0.858(4) D and μb=0.027(10) D for (H2 CO)2 and μa =0.908(4) D and μb=0.095(4) D for (D2CO)2. The geometry obtained from fitting the derived moments of inertia has the planes of the two monomer units perpendicular in a nearly antiparallel orientation of the CO groups with a center-of-mass distance of 3.046(17) Å. The shortest carbon to oxygen distance (2.98 Å) and hydrogen to oxygen distance (2.18 Å) between the monomer units are indicative of a dual bond interaction to form a ring structure.