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 $^1$ NH ( $v$ =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 $.1$ NH 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.