Knowledge Bank

The infrared absorption spectrum of acetylene-carbon monoxide, obtained in the three micron wavelength region from a pulsed molecular beam, indicates that this is a linear van der Waals complex. The spectrum is quite similar to that of acetylene-nitrogen. Excited state perturbations are present, but acetylene-carbon monoxide does not exhibit the hot bands found in HCCH-NN. The vibrational origin is at $3279.9cm-1$ and the ground state B value is 1497 MHz. This corresponds to a separation of 5.011 A for the monomer centers of mass. The spectrum cannot directly distinguish between the HCCH-CO and the HCCH-OC configurations. However, the HCCH-CO geometry produces a van der Waals bond 0.1 A shorter than the sum of van der Waals radil, while the HCCH-OC structure would have a bond length 0.3 A longer than the sum of van der Waals radil. Distributed multiple analysis also strongly favors the HCCH-CO configuration.