Time-resolved infrared diode laser spectroscopy of the ν1 band of the iron carbonyl radical (FeCO) produced by the ultraviolet photolysis of Fe(CO)5

Abstract

The infrared spectrum of the iron carbonyl radical FeCO generated by the 193 nm excimer laser photolysis of iron pentacarbonyl Fe(CO)5 was observed by time-resolved diode laser spectroscopy. The 85 lines, mostly observed as triplets split by the electron spin-spin interaction, were assigned to the ν1 (CO stretch) band of FeCO. The electronic ground state of FeCO was confirmed experimentally to have 3Σ− symmetry. Molecular constants in the ground and ν1 vibrational states were derived from an analysis of the infrared spectrum combined with pure rotational lines in the lowest spin component Ω=0 observed by Fourier transform microwave (FTMW) spectroscopy. The rotational and centrifugal distortion constants in the ground state were determined as B0=4364.266(55) MHz and D0=1.378(25) kHz, where the figures in parentheses are standard errors to be attached to the last digit. The spin-spin and spin-rotation coupling constants are λ0=663.1(40) GHz and γ0=−974(27) MHz, respectively. The origin of the ν1 vibrational band determined is 1946.470 60(12) cm−1, which is consistent with the value derived from photodetachment spectroscopy of the FeCO− anion. The collisional quenching rate of FeCO by Fe(CO)5 was measured to be 1.13(4)×10−10 cm3 molec −1 s−1 by a kinetic study.