15min:

KEIICHI TANAKA, MITSUHIRO NAKAMURA, MITSUAKI SHIRASAKA AND TAKEHIKO TANAKA, Department of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki, Higashiku, Fukuoka 812-8581, Japan, and Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan.

The rotational spectrum of iron carbonyl radical FeCO in the ₂ bending vibrational state of the ground X^3- electronic state was observed in the millimeter-wave region. The radical was produced by a dc discharge of iron pentacarbonyl Fe(CO)₅. Seven rotational lines, split into sextet by the electron spin-spin interaction and \Lambda-type dobling, were identified in the frequency region of 154-254 GHz. Molecular constants derived, the rotational and centrifugal distortion constants, the spin-spin coupling constant \lambda₀=679.37(291) GHz and the spin-rotation coupling constant \gamma₀=-1180.0(19) MHz, are reasonably similar to those of the ground state . Although the electronic state is ^3-, a large spin-orbit coupling constant A=14.0746(57) GHz was derived, indicating the vibronic coupling with the ³ electronic state located about 6500 cm^-1 above the ground state. From the \Lambda-type doubling, large interaction constants, o=-18.2899(55) GHz, p=-355.36(64) MHz, and q=9.5167(69) MHz, were determind, where the figures in parentheses are a standard error to be attached to the last digits.