Electron-atom Compton profiles due to the intramolecular motions of the H and D atoms in HD.

We report an atomic momentum spectroscopy (AMS) experiment on HD, performed at a scattering angle of 135° and at an incident electron energy of 2.0 keV. The electron-atom Compton profiles due to the intramolecular motions of the H and D atoms in HD were obtained.

Asymptotic behavior of the electron-atom Compton profile due to the intramolecular H-atom motion in H.

We report the asymptotic behavior of the electron-atom Compton profile due to the intramolecular H-atom motion in H. The experiment has been performed at a scattering angle of 135° and at incident electron energies from 1.0 to 2.

Electronic State and Photophysics of 2-Ethylhexyl-4-methoxycinnamate as UV-B Sunscreen under Jet-Cooled Condition.

The title compound, 2-ethylhexyl-4-methoxycinnamate (2EH4MC), is known as a typical ingredient of sunscreen cosmetics that effectively converts the absorbed UV-B light to thermal energy. This energy conversion process includes the nonradiative decay (NRD): - isomerization and finally going back to the original structure with a release of thermal energy. In this study, we performed UV spectroscopy for jet-cooled 2EH4MC to investigate the electronic/geometrical structures as well as the NRD mechanism.

The direct observation of the doorway nπ* state of methylcinnamate and hydrogen-bonding effects on the photochemistry of cinnamate-based sunscreens.

The electronic states and photochemistry including nonradiative decay (NRD) and trans(E) → cis(Z) isomerization of methylcinnamate (MC) and its hydrogen-bonded complex with methanol have been investigated under jet-cooled conditions. S1(1nπ*) and S2(1ππ*) are directly observed in MC. This is the first direct observation of S1(1nπ*) in cinnamate derivatives.

Different photoisomerization routes found in the structural isomers of hydroxy methylcinnamate.

An experimental and theoretical study has been carried out to elucidate the nonradiative decay (NRD) and trans(E) → cis(Z) isomerization from the S1 (1ππ*) state of structural isomers of hydroxy methylcinnamate (HMC); ortho-, meta- and para-HMC (o-, m- and p-HMC). A low temperature matrix-isolation Fourier Transform Infrared (FTIR) spectroscopic study revealed that all the HMCs are cis-isomerized upon UV irradiation. A variety of laser spectroscopic methods have been utilized for jet-cooled gas phase molecules to investigate the vibronic structure and lifetimes of the S1 state, and to detect the transient state appearing in the NRD process.

Detection of the Excited-State NH (Ã A) in the Ultraviolet Photodissociation of Methylamine.

Ion-imaging and dispersed fluorescence spectroscopy are employed for the photodissociation dynamics study of methylamine in the photolysis wavelength range 205-213 nm. The methyl radical product is found to populate a wide range of ro-vibrational states, among which the CH fragment generated in the v = 0 state shows a bimodal kinetic energy distribution. The internal energy analysis of the NH counterproduct indicates that a lower kinetic energy component, which was observed only with the CH(v=0) fragment, energetically matches the electronically excited ÃA state.

Multistep Intersystem Crossing Pathways in Cinnamate-Based UV-B Sunscreens.

The nonradiative decay pathways of jet-cooled para-methoxy methylcinnamate (p-MMC) and para-methoxy ethylcinnamate (p-MEC) have been investigated by picosecond pump-probe and nanosecond UV-Deep UV pump-probe spectroscopy. The possible relaxation pathways were calculated by the (time-dependent) density functional theory. We found that p-MMC and p-MEC at low excess energy undergo multistep intersystem crossing (ISC) from the bright S (ππ*) state to the lowest triplet T (ππ*) state via two competing pathways through the T state in the time scale of 100 ps: (a) stepwise ISC followed after the internal conversion (IC) from S to the dark nπ* state; (b) direct ISC from the S to T states.