Knowledge Bank

The $P=O(\nu 2)$ stretching fundamental of the transient molecule cis-HOPO has been measured using high resolution infrared diode laser absorption spectroscopy. The molecule was formed in a flow system by reacting white phosphorus vapour and the products of a microwave discharge through a mixture of hydrogen and oxygen. Over 300 lines have been assigned between $1242cm-1$ and $1267cm-1$. The band has the structure of an a-type transition of an asymmetric rotor. Most of the assigned lines were included in a least squares fit using Watson's A-reduced Hamiltonian. The band origin is $1258.540021(12)cm-1$. The rotational constants are in satisfactory agreement with those from Density Functional Theory and with those predicted from a comparison with the nitrogen analogue, cis-HONO:$A0=1.255036(55)$, $B0=0.3188211(99)$, $C0=0.2533085(91)A1=1.250424(55)$, $B1=0.3181419(96)$, $C1=0.2526089(96)$ Many of the remaining, unfitted lines are perturbed, particularly around $Ka=7$. The source of the perturbation will be considered.