Spectroscopy and photodissociation dynamics of hydroxyethyl radicals

The electronic spectroscopy and dissociation dynamics of 1- and 2- hydroxyethyl radicals were investigated using a combination of Resonance Enhanced Multiphoton Ionization (REMPI) and time-of-flight (TOF) detection of H and D photofragments.;The 3s and 3pz Rydberg states of CH3CHOH, CH 3CHOD, and CD3CHOH in the region 19,400--37,000 cm -1 were studied in a molecular beam. Absorption to the structureless 3s Rydberg state begins at 19,600 cm-1 though no REMPI spectrum is observed due to the fast predissociative nature of the state. Instead, the onset is detected using photofragment spectroscopy of H and D atoms. The electronic transition has a perpendicular transition moment, analogous to CH2OH. The onset of the predissociative 3pz state can be detected via REMPI, and is observed at 32360 cm-1. Photofragments detected from dissociation of this state show no recoil anisotropy. However, the beta parameter becomes more negative (indicative of a perpendicular electronic transition moment) as the excitation energy is decreased. The transition becomes more anisotropic as the energy decreases through the predicted region of the 3px Rydberg state towards the onset of the 3s state. The onset of the transition to the 3px state cannot be identified due to the large background signal from the 3s state. The translational energy distributions of H and D atims indicates that both the O-H(D) and C (2)-H(D) bonds can be broken at sufficiently high energies.;The ground state photodissociation dynamics of CD2CD 2OH radical were studied to determine product branching ratios and look for evidence of vinyl alcohol (CD2CDOH) product. Deuterated 2-hydroxyethyl radical (CD2CD2OH) was generated from photodissociation of the BrCD2CD2OH precursor by cleaving the Br-C bond at the wavelengths 202, 205, 210, and 215 nm. The energy left in the CD 2CD2OH radical after breaking this bond led to the spontaneous dissociation of the radical. The presence of acetaldehyde and vinyl alcohol products was inferred by monitoring the velocity distribution of the D atom co-fragment in the dissociation, and using conservation of energy to determine the identity of the molecular fragment. Different photolysis wavelengths were used to determine whether an obvious change in branching ratio between D and OH dissociation products would become evident as less energy for dissociation became available to the system. No precipitous drop in D products was seen toward longer photolysis wavelengths. However, a high velocity tail became apparent at longer wavelengths, indicating the onset of 2-photon processes at these energies. These processes are proposed to be owed to two phenomena: an absorption by the radical beginning at 210 nm, and lengthening of the lifetime of the excited radical as the available energy above the centrifugal barrier becomes smaller.;Both acetaldehyde and vinyl alcohol products were seen in the dissociation of CD2CD2OH. In agreement with RRKM calculations, vinyl alcohol products are expected to constitute the majority of the dissociations to D + molecular co-fragment.