Time-resolved infrared diode laser spectroscopy of the ν3 band of the jet-cooled Fe(CO)2 radical produced by ultraviolet photolysis of Fe(CO)5

Abstract

The infrared spectrum of the iron dicarbonyl radical Fe(CO)2 produced in a supersonic jet expansion by the excimer laser photolysis of iron pentacarbonyl Fe(CO)5 was observed by time-resolved infrared diode laser spectroscopy. About 170 transitions, each split into one or two fine structure components, were assigned to the ν3 (CO antisymmetric stretch) band of Fe(CO)2. The assignment was greatly facilitated by spectral simplification caused 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∞h symmetry and that the electronic ground state is of 3Σg− symmetry. The rotational and centrifugal distortion constants in the ground state were determined to be B0=1414.675(46) MHz and D0=0.3077(74) kHz, respectively. The spin–spin interaction constants obtained, λ0=655.3(42) GHz, is comparable with that of the FeCO radical, λ0=684.470(51) GHz. The ν3 band origin was determined to be 1928.184335 (82) cm−1. The figures in parentheses are uncertainties (1σ) in units of the last digit.

Time-resolved infrared diode laser spectroscopy of the ν1 (C–O stretch) band of the CoCO radical

“…Extensive spectroscopic and kinetic studies have been reported on unsaturated iron carbonyl complexes Fe(CO) n (n ¼ 1 À 4) [1][2][3][4], because they are prototypical examples of transition metal carbonyl radicals M n (CO) m [4][5][6][7][8][9][10][11][12][13][14][15], where M represents a transition metal element. In our previous papers, for example, we have reported the infrared diode laser spectroscopy of the m 1 (C-O stretch) band [1] and the millimeter-wave spectroscopy [2] of the iron monocarbonyl radical (FeCO) generated by the 193 nm ArF excimer laser photolysis of Fe(CO) 5 .…”

“…The observed spectral lines, split as triplets by the spin-spin interaction, provided a direct evidence for the 3 R À electronic ground state of FeCO to settle the controversy whether the ground electronic state of this radical is 3 R À or 5 R À [16][17][18][19][20][21][22]. We also combined the supersonic jet technique with the diode laser spectroscopy to observe the jet-cooled iron dicarbonyl radical Fe(CO) 2 [3]. Simplification of the spectrum caused by the jet cooling facilitated the assignment of the m 3 (C-O antisymmetric stretch) band spectrum of Fe(CO) 2 , and the missing of lines at alternate J quantum numbers observed in each spin component confirmed that the Fe(CO) 2 radical is linear and symmetric ðD 1h Þ and that the electronic state is of 3 R À g symmetry.…”

“…In the gas phase, infrared spectra of Co(CO) n , produced by the photolysis of cobalt tricarbonyl nitrosyl Co(CO) 3 NO with the KrF excimer laser (248 nm), were reported in 1986 by Rayner et al [23]. They also studied the kinetics for the reaction of cobalt carbonyl radicals Co(CO) n with the parent molecule Co(CO) 3 NO and CO.…”

“…They also studied the kinetics for the reaction of cobalt carbonyl radicals Co(CO) n with the parent molecule Co(CO) 3 NO and CO. The spectrum observed at 1952 cm À1 was assigned to the m 1 band of CoCO based on the reported results of the Ar matrix study [14].…”

“…The spectrum observed at 1952 cm À1 was assigned to the m 1 band of CoCO based on the reported results of the Ar matrix study [14]. Wang et al [24] studied products of the photolysis of Co(CO) 3 NO with tripled (355 nm) and quadrupled (266 nm) Nd:YAG laser, and assigned the spectrum observed at 1956 cm À1 to the C-O antisymmetric stretch of Co(CO) 2 , differently from the assignment by Rayner et al to the C-O stretch of CoCO [23]. According to Wang et al, predominant products of the 355 nm photolysis are Co(CO) 3 and Co(CO) 2 NO with the branching ratio of ca: 3:2, while the 266-nm photolysis yields Co(CO) 2 and NO-retaining products.…”