Knowledge Bank

The $OC-Br2$ van der Waals complex was observed in a 5''-pulsed-slit free jet expansion. The complex was detected by the IR absorption in the vicinity of 1-0 vibrational transition of C-O. Four isotopic progressions were recorded in the spectra. The rotational structure was consistent with a linear $OC-Br2$. The spectra were well-fitted by semirigid-rotor linear molecule model, the rotational constants for $OC-Br279,OC-Br79Br81,OC-Br81Br79$ and $OC-Br281$ isotopomers were obtained. The band origins of $OC-Br2$ were found to be 2152.83836(17), 2152.83929(16), 2152.84117(15) and $2152.84209(13)cm-1$ for the isotopomers of $OC-Br79,OC-Br79Br81,OC-Br81Br79$ and $OC-Br281$, respectively. From the isotope substituted rotational constants, the distances of the centers-of-mass of CO and $Br2$ were calculated to be 4.864 {\AA} and 4.875 {\AA} for the excited and ground state, respectively. The van der Waals bond formation siginficantly perturbed both the CO and $Br2$ bond lengths. In the ground state, the $C-O$ bond of the complex was 0.027 {\AA} shorter than that of the uncomplexed CO, while the Br-Br distance of the complex was 0.037 {\AA} longer than the bond length of free $Br2$.