1,720,984 research outputs found
Observation of the Stark effect in upsilon(+)=0 Rydberg states of NO: a comparison between predissociating and bound states
No full textThe Stark spectra of Rydberg states of NO below the ?+ = 0 ionization limit, with principal quantum numbers n = 25–30, have been investigated in the presence of dc electric fields in the range 0–150 V cm?1. The Stark states were accessed by two-colour, double-resonance excitation via the ?' = 0, N' = 0 rovibrational state of the A2?+ state. The N(2D) atoms produced by predissociation were measured by (2 + 1) resonance-enhanced multiphoton ionization, and compared with pulsed-field ionization spectra of the bound Rydberg state population (Patel et al 2007 J. Phys. B: At. Mol. Opt. Phys. 40 1369).<br/
Controlling the angular momentum composition of a Rydberg electron wave packet
No full textSequences of phase-locked laser pulses have been employed to control the orbital angular momentum character of an electron wave packet, which is initially created from a superposition of s and d Rydberg series. By an intelligent choice of phase, which depends on the excitation energy and the quantum defects, we are able to selectively pump down either all or a fraction of one or other angular momentum component, and by employing multichannel quantum-defect theory we are able to analyze the quantum-state distribution in detail
Frequency doubling and Fourier domain shaping the output of a femtosecond optical parametric amplifier: easy access to tuneable femtosecond pulse shapes in the deep ultraviolet
No full textTuneable, shaped, ultraviolet (UV) femtosecond laser pulses are produced by shaping and frequency doubling the output of a commercial optical parametric amplifier (OPA). A reflective mode, folded, pulse shaping assembly employing a spatial light modulator (SLM) shapes femtosecond pulses in the visible region of the spectrum. The shaped visible light pulses are frequency doubled to generate phase- and amplitude-shaped, ultrashort light pulses in the deep ultraviolet. This approach benefits from a simple experimental setup and the potential for tuning the central frequency of the shaped ultraviolet waveform. A number of pulse shapes have been synthesised and characterised using cross-correlation frequency resolved optical gating (XFROG). This pulse shaping method can be employed for coherent control experiments in the ultraviolet region of the spectrum where many organic molecules have strong absorption bands
Controlling the radial dynamics of Rydberg wavepackets in Xe using phase-locked optical pulse sequences
No full textWe employ a sequence of two phase-locked optical pulses, separated by half a classical orbit period, to control the radial dynamics of electron wavepackets in Xe. We eliminate either even or odd principal quantum number states from the wavepacket and distinguish between these systems by looking at the wavepacket spectrum at different partial revivals. The experimentally observed dynamics are compared with calculations based on multichannel quantum defect theory and the observations are interpreted in terms of the time and phase evolution of the population amplitudes of the Rydberg states contributing to the wavepacke
Ultrafast dynamics of the S(1) excited state of benzene
No full textWe investigate the ultrafast intramolecular dynamics of electronically and vibrationally excited benzene using time-resolved photoelectron spectroscopy and quantum dynamics simulations. In addition to an ultrafast initial decay, we observe an oscillation between two states. We interpret this data in terms of excited state population moving away from the Franck–Condon region towards the singlet–singlet conical intersection with the ground-state, where ultrafast intersystem crossing from the initially populated singlet state to an optically dark triplet state is enhanced. Our results challenge the currently accepted view that intramolecular processes in hydrocarbons which involve a change of spin are negligibly slo
Observation and control of dissociating and autoionizing Rydberg electron wave packets in NO
No full textThe dynamics of predissociating Rydberg electron wave packets are observed using the optical Ramsey method. The time-resolved spectra are hydrogenic and are very well modeled by assuming that only one p Rydberg series contributes to the dynamics. This is in contrast with previous observations of autoionizing Rydberg electron wave packets [Phys. Rev. Lett. 83, 2552 (1999)], which show quite dramatic deviations from hydrogenic behavior above the Born–Oppenheimer limit. The origin of these deviations lies in the interplay between electronic and molecular phase. By exploiting these phases we are able to control the ratio of predissociaton to autoionization
Competing ultrafast intersystem crossing and internal conversion in the "channel 3" region of benzene
Full text linkWe report new, detailed, femtosecond time-resolved photoelectron spectroscopy experiments and calculations investigating the competition between ultrafast internal conversion and ultrafast intersystem crossing in electronically and vibrationally excited benzene at the onset of “channel 3”. Using different probe energies to record the total photoelectron yield as a function of pump–probe delay we are able to confirm that S1, T1 and T2 electronic states are involved in the excited state dynamics. Time-resolved photoelectron spectroscopy measurements then allow us to unravel the evolution of the S1, T1 and T2 components of the excited state population and, together with complementary quantum chemistry and quantum dynamics calculations, support our earlier proposal that ultrafast intersystem crossing competes with internal conversion (Chem. Phys. Lett., 2009, 469, 43).<br/
A RAIRS, TPD and femtosecond laser-induced desorption study of CO, NO and coadsorbed CO + NO on Pd(111)
Full text linkHere we present a systematic study of the adsorption and laser induced desorption of CO, NO and CO + NO from a Pd(111) surface at a number of different coverages. We begin by characterising the surfaces using reflection-absorption infrared spectroscopy (RAIRS) and temperature-programmed desorption (TPD). Experiments show that NO displaces pre-adsorbed CO considerably, but that CO has a much smaller effect on pre-adsorbed NO. In both cases, the preferred binding sites of CO are occupied by NO, displacing it to less favourable adsorption sites. Femtosecond laser induced desorption (fs-LID) shows that desorption of CO on Pd(111) follows a power law and is fairly independent of CO coverage, but for NO on Pd(111) we observe a clear deviation from a power law curve at higher coverages, with saturation being observed. This suggests that the cross-section for LID of NO is much larger than that for CO and that NO on Pd(111) is more photoactive than CO on Pd(111). Interestingly, for CO + NO on Pd(111) we find that coadsorption has a strong influence on the photodesorption process and that the structure of the overlayer is also important in controlling the photodesorption products, regardless of the order in which the two molecules are dose
Marriage record of Pope, W. C. and Fielding, Minnie
No full textMarriage license for W.C. Pope and Minnie Fielding. H.H. Kissyere was the Notary Public
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