In molecule optics, a matter wave of molecules is manipulated by a molecule-optical component made out of external, typically radiative, fields. The molecule-optical index of refraction, n, for a nonresonant IR laser pulse focused onto a molecular beam can be obtained from the energy conservation and wave properties of molecules. Experimentally measured values of n for benzene and nitric oxide agreed well with the calculated values. Since n depends on the properties of molecules as well as those of the laser field, a molecule prism composed of the focused nonresonant laser field can separate a multi-component molecular beam into several components according to their molecule-optical refractive indices n. We obtained a chromatographic resolution of 0.62 for the spatial separation of a mixture beam of benzene and nitric oxide using a focused Nd:YAG laser pulse as a molecule prism.

The photodissociation of t-C 4 H 9 I has been studied at 277 and 304 nm in a supersonic molecular beam. The fragments (I and t-C 4 H 9 radical) are selectively ionized by resonance-enhanced multiphoton ionization and then projected onto a two-dimensional position-sensitive detector to obtain their translational energy and angular distributions. The energy distribution is found to consist of three components: one Maxwell-Boltzmann and two Gaussian distributions. Their anisotropy parameters range from 0.7 to 1.6 and display a parallel transition characteristic, where the greater the kinetic energy of the component, the stronger its anisotropy. From present and previous work, these three components are interpreted in terms of three independent reaction paths on an excited potential energy surface: (1) the prompt dissociation along the C-I stretching mode for the high-energy component, (2) the repulsive mode along the C-I stretching, coupled with some bending motions for the medium-energy component, and (3) the indirect dissociation, probably due to large contribution of the bending motions for the low-energy component. Relative quantum yields for I( 2 P 3/2 ) at 277 and 304 nm have been determined and found to be 0.93 ( 0.03 and 0.92 ( 0.04, respectively. Experiments have shown that t-C 4 H 9 I has the highest curve-crossing probability from the 3 Q 0 to 1 Q 1 state among low-carbon alkyl iodides. The extensive vibrational coupling between two states in the proximity of a crossing point supports this interpretation.

A molecular lens of the nonresonant dipole force formed by focusing a nanosecond IR laser pulse has been applied to benzene and CS 2 molecular beams. Using the velocity map imaging technique for molecular ray tracing, characteristic molecular lens parameters including the focal length ͑f ͒, minimum beam width ͑W͒, and distance to the minimum beam width position ͑D͒ were determined. The laser intensity dependence of the observed lens parameters was in good agreement with theoretical predictions. W was independent of the laser peak intensity (I 0 ), whereas f and D varied linearly with 1/I 0 . The differences in lens parameters between the molecular species were well correlated with the polarizability per mass values of the molecules. A high chromatographic resolution of Rsϭ0.84 was achieved between the images of benzene molecular beams undeflected and deflected by the lens. The possibilities for a new type of chromatography are discussed.

A cylindrical molecular lens is formed by focusing a nanosecond IR laser pulse. Trajectories of a CS 2 molecular beam deflected by the lens are traced using the velocity map imaging technique. The characteristic lens parameters including the focal length, minimum beam width, and distance to the minimum-width position are determined. The laser intensity dependence of the parameters is in good agreement with theoretical predictions. Exciting possibilities for molecular optics and a new type of optical chromatography are opened up.

Articles you may be interested inEffect of laser spectral bandwidth on coherent control of resonance-enhanced multiphoton-ionization photoelectron spectroscopy

Photodissociation of n-alkyl iodides and CF3I has been studied using state-selective ionization and pulsed-field time-of-flight (TOF) mass spectrometry. The (2+1) resonance-enhanced multiphoton ionization cross-section ratio of I(2P1/2) and I(2P3/2) is measured from I2 photodissociation in the 304 nm region. Using this ratio, the relative populations of I(2P1/2) and I(2P3/2) by a pure parallel excitation to the 3Q0 state of n-alkyl iodides and CF3I are obtained. This method can exclude the effects of clusters and spectrum overlap in different dissociation paths from branching ratio calculations. The product quantum yield of I(2P3/2) obtained from branching ratio reveals the 3Q0–1Q1 curve crossing probability—which increases from 0.70 for CH3I to 0.86 for n-C4H9I (with recoil velocity decrease of fragments at the curve crossing point). The potential energies at the crossing point and the Landau–Zener parameters ζ, calculated from our modified model, are 385 kJ/mol and 1100 m/s for n-alkyl iodides, and 391 kJ/mol and 177 m/s for CF3I, respectively.

No abstract

The multiplet state distribution of O(3 P J ) produced in the 193 nm photodissociation of SO2The photodissociation of CF 3 I cooled in a supersonic molecular beam has been investigated at 277 nm by state-selective photofragment imaging. Fragmented iodine atoms of two spin-orbit states are state-selectively ionized and projected onto a two-dimensional position-sensitive detector, to obtain their speed and angular distribution. The anisotropy parameter for an excited iodine atom I*( 2 P 1/2 ), ␤(I*), is found to be 1.83 and is consistent with a dissociation lifetime in the order of 150-350 fs from rotational correlation function. Contrary to earlier reports, the parallel-like distribution for the ground state iodine atom I( 2 P 3/2 ) at this wavelength, shows a more favorable curve-crossing dissociation path ͑68%͒ from 3 Q 0 to 1 Q 1 and a less favorable direct dissociation path ͑32%͒ from 3 Q 1 . The recoil energy distribution of I is found to be broader than that of I* and is correlated with a variety of energy disposal channels by an e symmetry vibration at the crossing point. The results are compared with previous works, and the strong photon energy dependence of the energy partitioning in CF 3 ϩI* channel and curve crossing are interpreted in terms of the final state interaction and curve crossing probability, respectively.