Knowledge Bank

The infrared spectrum of carbonyl sulfide dimer, $(OCS)2$, has been recorded by observing the absorption of diode laser radiation in a pulsed molecular beam. The observed signals, in the carbonyl stretching region of the infrared spectrum, are from a perpendicular band of a quite asymmetric prolate rotor. Energy levels in the ground state with odd K*** values are missing, which requires $(OCS)2$ to have a center of symmetry. The vibrational origin occurs at $2072.007cm-1$, and the rotational constants are $A\prime \prime -3075.B\prime \prime =1263,C\prime \prime -894,A\prime =3068,B\prime -1259$, and $C\prime =892$ MHz. Centrifugal distortion constants, constrained to be equal for both vibrational states, were also obtained in the data analysis. The vibrational origin is shifted to higher frequency by $10cm-1$, relative to the isolated monomer transition. The rotational constants and missing levels are consistent with a geometry having parallel monomer axen and opposite monomer orientation. The perpendicular separation of the monomer axes is 3.636 A, and the monomer centers of mass are nearly opposite one another. The horizontal separation of the centers of mass is $\pm 0.294\backslash AA$.