Knowledge Bank

Infrared spectrum of CoNO has been measured in low temperature Ar matrix and the $\nu 1$ and $\nu 3$ band origins were reported to be 1761.0 and $620.1cm-1$ $respectively.a$ Recent DFT calculations suggested that the linear form $(X1\Sigma )$ and bent form $(X3A\prime )$ of CoNO have almost the same $energies.a$ In the present study, the pure rotational spectrum of CoNO generated in a supersonic jet expansion by ultraviolet photolysis of $Co(CO)3NO$ was observed in the millimeter-wave region. This is the first observation of the rotationally resolved spectrum of the transition metal nitrosyl in the gas phase. Seven rotational transitions (from $J=6-5$ to $12-11$) were measured in the frequency region of $56-112$ GHz. Each rotational transition was split into $8-11$ components due to hyperfine interaction of the Co $(I=7/2)$ nucleus. The spectrum was analyzed to determine molecular constants, including the rotational constant B, centrifugal distortion constant D, nuclear quadrupole interaction constant eQq, and nuclear spin-rotation interaction constant $CI$. From the observed spectral pattern, it is confirmed that CoNO has a linear structure and the electronic ground state is $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma$. The Co-N bond length was calculated to be 1.588 \AA from the rotational constant, which is by 0.1 \AA shorter than the Co-C bond length of CoCO. Measurement of rotational transitions in the $\nu 2$ vibrationally excited state is in progress.