Knowledge Bank

The infrared spectrum of carbon dioxide-acetylene has been recorded in the three micron wavelength region by observing direct absorption of color center laser radiation by a pulsed molecular beam. The spectrum is that of a perpendicular transition in a moderately asymmetric prolate rotor. The vibrational origin is $3281.740cm-1$ and the rotational constants are $A\prime \prime =8876,B\prime \prime =2859,C\prime \prime =2155,A\prime =8864,B\prime =2855$, and $C\prime =2154$ MHz. The axes of the two monomer molecules are parallel and the complex has $C2v$ symmetry. The separation of the monomer units is 3.285 A. This geometry is readily predicted by considering the quadrupole-quadrupole interaction. Since the monomers have quadrupole moments of opposite sign, this configuration places positive regions of each monomer opposite negative regions of the other. A more detailed model of electrostatic interactions between distributed multipole moments will also be discussed.