Infrared diode laser spectroscopy of jet-cooled NiCO, Ni(CO)?(??CO), and NI(CO)?(c??O)

Gas phase infrared spectroscopic investigations of the CO vibration of jet-cooled NiCO, Ni(CO)3(13CO), and Ni(CO)3(C18O) are reported. The spectra were obtained using a recently assembled pulsed-discharge slit-jet IR diode laser spectrometer. The rotationally resolved spectrum of NiCO was collected as it was formed in the discharge, while the spectra of Ni(CO)3(13CO) and Ni(CO)3(C18O) were recorded as they were destroyed. For NiCO, band origins of 2010.692 89(34) and 2010.645 28(23) cm?1 were measured, along with values of B0=0.151 094(7) and 0.149 597(6) cm?1 and B1=0.150 244(7) and 0.148 742(6) cm?1 for 58NiCO and 60NiCO, respectively. The B0 values for these isotopologs were used to determine the two bond lengths in NiCO, giving r0 (Ni?C)=1.641(40) ? and r0 (C?O)=1.193(53) ?, in agreement with recent microwave measurements. The constants determined for Ni(CO)3(13CO) were ?0 =2022.075 753(95) cm?1, B"=0.034 736(2) cm?1, and B"=0.034 688(2) cm?1. For Ni(CO)3(C18O), ?0=2021.936 83(18) cm?1, B"=0.033 764(4) cm?1, and B'=0.033 710(4) cm?1 were obtained. From these rotational constants, bond lengths of r0 (Ni?C)=1.839?0.007 ? and r0 (C?O)=1.121?0.010 ? were obtained. These values are discussed in relation to the bond lengths measured by electron and x-ray diffraction methods.