Time-resolved infrared diode laser spectroscopy of the nu(3) band of the jet-cooled Fe(CO)(2) radical produced by ultraviolet photolysis of Fe(CO)(5)

The infrared spectrum of the iron dicarbonyl radical Fe(CO)(2) produced in a supersonic jet expansion by the excimer laser photolysis of iron pentacar bonyl Fe(CO)(5) was observed by time-resolved infrared diode laser spectros copy. About 170 transitions, each split into one or two fine structure comp onents, were assigned to the nu(3) (CO antisymmetric stretch) band of Fe(CO )(2). The assignment was greatly facilitated by spectral simplification cau sed by rotational as well as vibrational cooling in the supersonic jet. It was observed that lines are missing at alternate J quantum numbers in each spin component, which confirmed that Fe(CO)(2) is a linear molecule with D- infinity h symmetry and that the electronic ground state is of (3)Sigma(g)( -) symmetry. The rotational and centrifugal distortion constants in the gro und state were determined to be B-0=1414.675(46) MHz and D-0=0.3077(74) kHz , respectively. The spin-spin interaction constants obtained, lambda(0)=655 .3(42) GHz, is comparable with that of the FeCO radical, lambda(0)=684.470( 51) GHz. The nu(3) band origin was determined to be 1928.184335 (82) cm(-1) . The figures in parentheses are uncertainties (1 sigma) in units of the la st digit. (C) 1999 American Institute of Physics. [S0021-9606(99)01833-4].