Knowledge Bank

Laser-induced fluorescence from the $(0.90\circ )$ level of the $A~2\Pi A\prime \prime$ state of the HCO radical has been detected following pulsed dye laser excitation of the (0,0,0) level of the $X~2A\prime$ state at 614.48nm. Fluoroescence emission from $A~\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\pi A\prime \prime HCO$ is extremely weak, due to the predissociation of all levels with $1\prime >0$. The HCO is generated by the photolysis of a 0.2 to 25 torr sample of acetaldehyde vapr at 300k using the 308 nm output of a XeCl excimer laser. Fluorescence excitation and dispersed emission spectra of $Lademann1$ is not observed. A determination was made of the vibrational frequency of the C-H stretch, $V1\prime \prime =2432cm-1+20cm-1$ for the first time in the gas phase, and it is close to the value of $2483cm-1$ determined in an Ar $matrix.2$ The fluorescence lifetime of $A~2\pi A\prime \prime HCO$ was measured to be nsec, and is shorter than the 46 nsec lifetime reported by Konig and $lademann.1$. The disappearance kinetics of the HCO radical was observed to be second-order in HCO.