Imaging HNCO Photodissociation at 201 nm: State-to-State Correlations between CO (X^1\Sigma^+) and NH (a^1\Delta)

The NH(a^1\Delta)+CO(X^1\Sigma^+) product channel for the photodissociation of isocyanic acid (HNCO) on the first excited singlet state S_1 has been investigated by means of time-sliced ion velocity map imaging technique at photolysis wavelengths around 201 nm. The CO product was detected through (2+1) resonance enhanced multiphoton ionization (REMPI). Images were obtained for CO products formed in the ground and vibrational excited state (v=0 and v=1). The energy distributions and product angular distributions were obtained from the CO velocity imaging. The correlated NH(a^1\Delta) rovibrational state distributions were determined. The vibrational branching ratio of ^1NH (v=1/v=0) increases as the rotational state of CO(v=0) increases initially and decreases afterwards, which indicates a special state-to-state correlation between the .1NH and CO products. About half of the available energy was partitioned into the translational degree of freedom. The negative anisotropy parameter \beta indicates that it is a vertical direct dissociation process.