Studies of the 193 nm photolysis of diethyl ketone and acetone using time-resolved Fourier transform emission spectroscopy

We have observed the infrared emission from the products of the 193 nm photolysis of diethyl ketone (3-pentanone) in comparison with acetone (2-propanone) using time-resolved Fourier transform spectroscopy. In the photolysis of diethyl ketone, two bands are apparent: The first, spanning the region 1950 to 2250 cm^-1, is assigned to CO rovibrational transitions; the other band, spanning the region 2800 to 3400 cm^-1 and not exhibiting resolved line structure, is assigned to the ethyl radical. Spectral simulations of the CO bands under conditions of minimal, but not negligible, relaxation produce a lower bound for the nascent CO rotational temperature of ∼2100 K. The CO vibrational population distribution varies slowly over the ∼80 μs time spanned by our experiment. Both the rotational and vibrational energies of CO exceed statistical partitioning in the dissociation of acetone. In comparison to the case of acetone, absolute energies in CO vibration and rotation decrease only modestly for diethyl ketone, corresponding to a dramatic increase in the excess above the statistically partitioned energies. Several simple dissociation models are compared to these results. None is fully satisfactory.