Study Of Photochemical Processes Research Articles

UV Photodesorption of Novel Molecular Beam Induced NO Layers on NiO(111)/Ni(111)

The photodesorption and photoreactivity of the molecular beam dosed NO/NiO(111)/Ni(111) system has been examined using high-resolution electron energy loss spectroscopy (HREELS). The molecular beam dosed surface exhibits three major vibrational peaks, which we attribute to a linear bonding NO species at 230 meV, a bent bonding NO species at 197 meV, and a stretching mode of NO 2 at 160 meV. UV photon irradiation causes the attenuation of these peaks accompanied by simultaneous emergence of a fourth vibrational peak at 215 meV. The emergence of this peak is explained by a mechanism of selective desorption of the original, linear-bound NO species and a reaccommodation of the beam-induced, bent NO structure to a new state on the lower coverage surface. The measured desorption cross sections and wavelength dependence are consistent with those of other studies of photochemical processes on such interfaces, indicating that photoinduced electron transfer from the substrate to the adsorbate is the mechanism responsible for the observed behavior.

Photochemical properties of carotenoids: What can we get from the VB model?

The empirical valence bond model, solved by the DMRG technique, is applied to the systematical study of the photochemical processes of carotenoids. The polyenes with five up to one hundred of C=C bonds are investigated. The probability of the state arrangement for the conjugated bond, Pij is evaluated. It is a parameter to correlate the bond lengths, and could also be applied to rationalizing the quantum yields of the photo-isomerization and the reaction constant of the quenching of singlet-oxygen happened to the external C=C bond of the carotenoids. The maximum reaction constant in long chain limit is determined as about 2.92×1010 L · mol-1 ·s-1

The analytic gradient for the equation-of-motion coupled-cluster energy with a reduced molecular orbital space: An application for the first excited state of formaldehyde

The analytic gradient method for the equation-of-motion coupled-cluster (EOM-CC) energy has been extended to employ a reduced molecular orbital (MO) space. The geometrical and the vibrational properties of the first excited singlet state of formaldehyde have been studied by using several different sizes of dropped MO space. It is shown that reliable results can be produced with high efficiency by employing the EOM-CC with a reduced MO space, which provides a new hierarchy in the study of photochemical processes in molecules.

Free‐floating drifter for photochemical studies in the water column

A free‐floating drifter was designed to directly determine in situ photochemical production rates, photolysis rates, and light fluxes in seawater. This drifter consisted of six trays that were suspended in series from a single buoy line. The trays were constructed so that the attached quartz vessels, containing filtered seawater, were exposed to both downwelling and upwelling irradiation. The quartz vessels were sealed at both ends with ribbed TFE Teflon stoppers that permitted multiple subsampling without introduction of a headspace. The free‐floating drifter was used to study photochemical processes in antarctic waters. It performed well during 12–15‐h deployments, even in rough seas with sustained winds between 15 and 26 m s−1. Although not tested here, the drifter should perform equally well in the study of photochemical processes in freshwater environments.