Photodissociation of laboratory oriented molecules: Revealing molecular frame properties of nonaxial recoil

We report the photodissociation of laboratory oriented OCS molecules. A molecular beam of OCS molecules is hexapole state-selected and spatially oriented in the electric field of a velocity map imaging lens. The oriented OCS molecules are dissociated at 230 nm with the linear polarization set at 45 degrees to the orientation direction of the OCS molecules. The CO(nu=0,J) photofragments are quantum state-selectively ionized by the same 230 nm pulse and the angular distribution is measured using the velocity map imaging technique. The observed CO(nu=0,J) images are strongly asymmetric and the degree of asymmetry varies with the CO rotational state J. From the observed asymmetry in the laboratory frame we can directly extract the molecular frame angles between the final photofragment recoil velocity and the permanent dipole moment and the transition dipole moment. The data for CO fragments with high rotational excitation reveal that the dissociation dynamics is highly nonaxial, even though conventional wisdom suggests that the nearly limiting beta parameter results from fast axial recoil dynamics. From our data we can extract the relative contribution of parallel and perpendicular transitions at 230 nm excitation.     

Laser excitation spectrum of PbO: Rotational analysis of the a(1)-X(0+) system

A flashlamp-pumped tunable dye laser has been used to investigate the a-X band system of PbO. Spectra with resolution adequate for rotational analysis were obtained by exciting a-X photoluminescence with the laser operating at a bandwidth of 0.2 cm^?1. The (3,1) and (4,1) bands have been rotationally analyzed, providing the rotational constants B₃ = 0.2389 ± 0.0002 cm^?1 and B₄ = 0.2374 ± 0.0002 cm^?1 for the a state. Observation of P, Q, and R branch structure confirms the assignment of the a state as a Hund's case (c), $\text{Ω}\text{= 1}$ state of PbO. Calculated combination defects having positive algebraic sign support the presence of a b(0^?) state approximately 350 cm^?1 above the a(1) state.     

Polarized Light and Quantum Mechanics: An Optical Analog of the Stern–Gerlach Experiment

Lecture demonstrations involving polarization of light are presented and discussed from the quantum theoretical point of view. The demonstrations clearly show that only two base states are required to describe the quantum state of a photon and they illustrate an optical analog of the Stern—Gerlach experiment that involved electrons.     

Light‐Driven Rotary Molecular Motors on Gold Nanoparticles

We report the synthesis of unidirectional light‐driven rotary molecular motors based on chiral overcrowded alkenes and their immobilisation on the surface of gold nanoparticles through two anchors. Using a combination of ¹H and ¹³C NMR, UV/Vis and CD spectroscopy, we show that these motors preserve their photochemical and thermal behaviour after they have been attached to gold nanoparticles. Furthermore, we describe the synthesis of ²H‐ and ¹³C‐labelled derivatives that were used to verify the unidirectionality of the rotary cycle of these motors both in solution and while grafted to gold nanoparticles. Taken together, these data support the conclusion that these motors maintain their unidirectional rotary cycle when grafted to the surface of small (ca. 2 nm) gold nanoparticles. Thus, continuous irradiation of the system under appropriate conditions leads to unidirectional rotation of the upper half of the molecules relative to the entire nanoparticle.