We have studied the photolysis of n-hexanal (CH3(CH2)(4)CHO) and n-heptanal (CH3(CH2)(5)CHO) at 5-nm intervals in the 280-330-nm region by using dye-laser photolysis combined with cavity ring-down spectroscopy. Their absorption cross sections have been obtained at each wavelength studied. The HCO radical is a photodissociation product of both aldehydes. The HCO radical quantum yields have been determined as a function of photolysis wavelength (A), aldehyde pressure, and nitrogen buffer gas pressure. The HCO radical yields decrease with increasing aldehyde pressure (0.5-8 Torr for n-hexanal and 0.5-4 Torr for n-heptanal) because of the increasing HCO + HCO, HCO + R, and HCO + RCHO reactions (R = n-C5H11 for n-hexanal and n-C6H13 for n-heptanal) at higher aldehyde pressures and because of quenching by ground-state aldehydes. After separating the contribution of HCO radical reactions, the aldehyde-pres sure quenching effect was still observed at all wavelengths. The HCO quantum yields and the ratios of quenching to unimolecular decay rate constants of excited aldehydes are given. The HCO quantum yields from n-hexanal photolysis are 0.12 +/- 0.01, 0.15 +/- 0.02, 0.14 +/- 0.02, and 0.10 +/- 0.01 at 305, 310, 315, and 320 nm, respectively, where the uncertainty (1sigma) represents experimental scatter. The corresponding HCO quantum yields from n-heptanal photolysis are 0.14 +/- 0.04, 0.15 +/- 0.06, 0.10 +/- 0.01, and 0.11 +/- 0.02, respectively. A comparison of the HCO radical yields from the wavelength-dependent photolysis of n-hexanal and n-heptanal with that from n-pentanal photolysis indicates that the HCO radical yields from aldehyde photolysis do not vary with chain length for aldehydes with chain lengths that are longer than or equal to five carbon atoms. The dependence of the HCO quantum yield on nitrogen buffer gas pressure was examined between 6 and 387 Torr; no dependence was observed. The end products from 308-nm excimer-laser photolysis of both aldehydes were measured by mass spectrometry and FTIR. Evidence has been obtained for the occurrence of the Norrish II channel, and the photocyclization channels for both aldehydes and their yields have been obtained.