Vector Correlation in the 225 nm Photodissociation of Cobalt Tricarbonyl Nitrosyl
The photochemistry of organometallic-nitrosyls has been widely investigated because of the importance of the nitric oxide ligand in biological systems and the unique electronic chemical properties of transition metal-NO compounds. In the ground state the Co-NO bond in Co(COhNO is linear. It has been proposed that Co(COhNO photodissociates through a bent CoNO transition state. It was the goal of this investigation to provide more direct evidence of the bent excited state transition by spectroscopically probing nascent NO+ upon dissociation. A three color photodissociation and 1+1' REMPI scheme was used for photodissociation and ionization: 225 nm laser light for dissociation of Co(COhNO, a tunable 224-227 nm stateselective probe of NO, and 308 nm for ionizing excited NO. The NO+ product ions were detected by photofragment ion imaging. The ion images were analyzed to determine the vector correlation and speed distribution of NO and to provide evidence for the proposed bent excited state. The velocity-mapped ion images displayed both a slow isotropic and a faster anisotropic speed distribution. The a nisotropic distribution depended upon the polarization of the lasers and the rotational transition being analyzed. A negative velocity-angular momentum correlation was found for P and Q branch transitions suggesting that v-,/with average correlations of -0.066 and -0.021 for P and Q (Ou + P21 and On + R12) branches respectively. In support of the experimental findings, OFT calculations reveal that a bent excited state is energetically favorable compared to its linear counterpart. Both the experimental data and OFT calculations provide evidence that the Co-NO bond bends in the excited state due to a Jahn-Teller distortion.