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i) IN THE GROUND AND VIBRATIONALLY EXCITED STATES.
MOTOKI NAKASHIMA, MASATO HAYASHI, KENSUKE HARADA AND KEIICHI TANAKA, Department of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki, Higashiku, Fukuoka 812-8581, Japan.
Rotational spectrum of the FeNO radical generated by the ultraviolet photolysis of Fe(CO)2(NO)2 was measured in the millimeter-wave region. The measurements were performed in the supersonic jet expansion with a millimeter-wave multi-reflection cell. Three rotational transitions (J = 9.5 - 8.5
11.5 - 10.5) in the
= 5/2 spin substate of the X2
i ground vibronic state were measured in the frequency region of 87-106 GHz. The rotational lines were split into 2 components (
F = 0,+1) due to the hyperfine interaction of the N(I = 1) nucleus. In the upper spin substate
= 3/2 (A SO ~ -417~ cm-1) of the electronic ground state, seven rotational transitions (J = 28.5 - 27.5
34.5 - 33.5) were measured with a conventional absorption cell (2.7 m in length) in the room temperature. Moreover, six rotational transitions (J = 28.5 - 27.5
33.5 - 32.5) in the
2 vibrationally excited state (for both P = 3/2 and 7/2 components) and the high-J lines of
= 5/2 spin substate of the ground state were also observed with the conventional absorption cell. Rotational line intensity of the
= 3/2 substate was about one tenth of that for the
= 5/2 substate because of the large spin-orbit interaction constant A SO. Molecular constants, including the rotational constant B, centrifugal distortion constant D, hyperfine constant a+bF/4+c/6, and vibration rotation constant
2, were determined by a least squares fitting of the observed spectrum. The electronic ground state of FeNO was confirmed to be X2
i as in the case of CoCO and the unpaired electron is localized almost in the 3 d orbital of Fe. The hyperfine constant of FeNO, a+bF/4+c/6 = -1.359(57) MHz, is much smaller than that of CoCO, 466.073(54) MHz. Rovibrational transitions were also observed by the infrared diode laser spectroscopy with the ultraviolet photolysis of Fe(CO)2(NO)2.