Laser-induced fluorescence instrument for the detection of CH₂O

An in situ formaldehyde (CH₂O) instrument requires the sensitivity to detect parts per trillion concentrations of CH₂O. Whereas traditional absorption spectroscopic techniques do not satisfy these sensitivity requirements, laser-induced fluorescence detection of CH₂O is a particularly attractive technique due to the high fluorescence efficiency of the excited state. Detection of CH₂O with LIF generally involves features near 355 nm, where dissociation of the excited state is lowest (∼ 30% photodissociation). Recent high-resolution (< 0.05 cm^-1) absorption measurements in our laboratory show that the features near 355 nm contain single rotational transitions and also that the high-resolution absorption cross sections for these transitions are considerably larger than reported from low-resolution measurements.