Microwave measurements and calculations for the glyoxylic acid – Formic acid hydrogen-bonded complex

The gas-phase doubly hydrogen-bonded glyoxylic acid - formic acid hydrogen-bonded complex was obtained by mixing a heated sample of glyoxylic acid with room-temperature formic acid in argon. High-level DFT and MP2 calculations with various basis sets were performed and the structures and rotational constants were determined for the lowest energy dimers of glyoxylic acid - formic acid. The microwave spectrum was measured in the 6-12 GHz frequency range using two Flygare-Balle type pulsed beam Fourier transform microwave (FTMW) spectrometers. The rotational constants were determined to have the following values: A = 5533.911(3), B = 923.3883 (5), and C = 792.1132(6) MHz using 18 transitions. B3LYP/ cc-pVQZ calculations for the lowest energy dimer yielded calculated rotational constants of A = 5551.2, B = 922.9 and C = 791.3 MHz.