Scattering of Stark-decelerated OH radicals with rare-gas atoms

We present a combined experimental and theoretical study on the rotationally inelastic scattering of OH (X\,^2\Pi_{3/2}, J=3/2, f) radicals with the collision partners He, Ne, Ar, Kr, Xe, and D$_2$ as a function of the collision energy between $\sim 70$ cm$^{-1}$ and 400~cm$^{-1}$. The OH radicals are state selected and velocity tuned prior to the collision using a Stark decelerator, and field-free parity-resolved state-to-state inelastic relative scattering cross sections are measured in a crossed molecular beam configuration. For all OH-rare gas atom systems excellent agreement is obtained with the cross sections predicted by close-coupling scattering calculations based on accurate \emph{ab initio} potential energy surfaces. This series of experiments complements recent studies on the scattering of OH radicals with Xe [Gilijamse \emph{et al.}, Science {\bf 313}, 1617 (2006)], Ar [Scharfenberg \emph{et al.}, Phys. Chem. Chem. Phys. {\bf 12}, 10660 (2010)], He, and D$_2$ [Kirste \emph{et al.}, Phys. Rev. A {\bf 82}, 042717 (2010)]. A comparison of the relative scattering cross sections for this set of collision partners reveals interesting trends in the scattering behavior.Comment: 10 pages, 5 figure

High-resolution infrared spectroscopy of O2H+ in a cryogenic ion trap

The protonated oxygen molecule, O2H+, and its helium complex, He-O2H+, have been investigated by vibrational action spectroscopy in a cryogenic 22-pole ion trap. For the He-O2H+ complex, the frequencies of three vibrational bands have been determined by predissociation spectroscopy. The elusive O2H+ has been characterized for the first time by high-resolution rovibrational spectroscopy via its nu(1) OH-stretching band. Thirty-eight rovibrational fine structure transitions with partly resolved hyperfine satellites were measured (56 resolved lines in total). Spectroscopic parameters were determined by fitting the observed lines with an effective Hamiltonian for an asymmetric rotor in a triplet electronic ground state, (X) over tilde (3)A '', yielding a band origin at 3016.73 cm(-1). Based on these spectroscopic parameters, the rotational spectrum is predicted, but not yet detected. Published by AIP Publishing

Infrared photodissociation of cold CH3+-He-2 complexes

A cryogenic 22-pole ion trap apparatus is used to probe weakly bound cold CH-Hecomplexes by IR action spectroscopy at 4K. The infrared photodissociation spectrum of the antisymmetric C-H stretching vibration is recorded in the range of 3102-3139cm(-1). A comparison between the experimental spectrum and a symmetric rotor Hamiltonian indicates that this band is strongly perturbed, but we report here a preliminary set of spectroscopic parameters. [GRAPHICS]

Double Resonance Rotational Spectroscopy of Weakly Bound Ionic Complexes: The Case of Floppy CH3+-He

A novel rotational spectroscopy method applicable to ions stored in cold traps is presented. In a double resonance scheme, rotational excitation is followed by vibrational excitation into a dissociative resonance. Its general applicability is demonstrated for the CH3+-He complex, which undergoes predissociation through its C-H stretching modes nu(1) and nu(3). High resolution rotational transitions are recorded for this symmetric top, and small unexpected splittings are resolved for K = 1. Advantages and potential future applications of this new approach are discussed

Frequency-domain interferometry for the determination of time delay between two extreme-ultraviolet wave packets generated by a tandem undulator

Abstract Synchrotron radiation, emitted by relativistic electrons traveling in a magnetic field, has poor temporal coherence. However, recent research has proved that time-domain interferometry experiments, which were thought to be enabled by only lasers of excellent temporal coherence, can be implemented with synchrotron radiation using a tandem undulator. The radiation generated by the tandem undulator comprises pairs of light wave packets, and the longitudinal coherence within a light wave packet pair is used to achieve time-domain interferometry. The time delay between two light wave packets, formed by a chicane for the electron trajectory, can be adjusted in the femtosecond range by a standard synchrotron technology. In this study, we show that frequency-domain spectra of the tandem undulator radiation exhibit fringe structures from which the time delay between a light wave packet pair can be determined with accuracy on the order of attoseconds. The feasibility and limitations of the frequency-domain interferometric determination of the time delay are examined

Quantum-state resolved bimolecular collisions of velocity-controlled oh with no radicals

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