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51.
Spesyvtsev R Kirkby OM Vacher M Fielding HH 《Physical chemistry chemical physics : PCCP》2012,14(28):9942-9947
Efficient electronic relaxation following the absorption of ultraviolet light is crucial for the photostability of biological chromophores, so understanding the microscopic details of the decay pathways is of considerable interest. Here, we employ femtosecond time-resolved photoelectron imaging to investigate the ultrafast intramolecular dynamics of aniline, a prototypical aromatic amine, following excitation just below the second absorption maximum. We find that both the second ππ* state and the Rydberg state are populated during the excitation process. Surprisingly, the dominant non-radiative decay pathway is an ultrafast relaxation mechanism that transfers population straight back to the electronic ground-state. The vibrational energy resolution and photoelectron angular distributions obtained in our experiments reveal an interesting bifurcation of the Rydberg population to two non-radiative decay channels. The existence of these competing non-radiative relaxation channels in aniline illustrates how its photostability arises from a subtle balance between dynamics on different electronically excited states and importantly between Rydberg and valence states. 相似文献
52.
53.
An intuitive scheme for controlling the quantum state composition of one-coordinate molecular wave packets is developed. The accumulated phase difference between the various components of the molecular wave packet is determined, and then a sequence of phase-locked optical pulses is employed to selectively enhance or depopulate specific vibrational states, or sets of vibrational states. The quantum state composition of the resulting wave packet, and the efficiency of the control scheme, is determined by calculating the multi-pulse response of the time-dependent vibrational state populations. 相似文献
54.
D. S. N. Parker A. D. G. Nunn R. S. Minns H. H. Fielding 《Applied physics. B, Lasers and optics》2009,94(2):181-186
Tuneable, 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.
D.S.N. Parker and A.D.G. Nunn contributed equally to this work. 相似文献
55.
Sequences 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. 相似文献
56.
Cameron KS Clark JK Cooper A Fielding L Palin R Rutherford SJ Zhang MQ 《Organic letters》2002,4(20):3403-3406
A series of per-6-substituted cyclodextrin derivatives was synthesized as synthetic host molecules for rocuronium, a steroidal muscle relaxant. By forming host-guest complexes with rocuronium, these cyclodextrin derivatives reverse the muscle relaxation induced by rocuronium in vitro and in vivo. The isothermal microcalorimetry data are consistent with the biological data supporting the encapsulation mechanism of action. Binary and biphasic complexes are reported with NMR experiments clearly showing free and bound rocuronium. [structure: see text] 相似文献
57.
After surveying the experimental evidence for concentration coupling in the shear banding of wormlike micellar surfactant
systems, we present flow phase diagrams spanned by shear stress Σ (or strain rate ) and concentration, calculated within the two-fluid, non-local Johnson-Segalman (d-JS-φ) model. We also give results for
the macroscopic flow curves Σ(ˉ,ˉφ) for a range of (average) concentrations ˉφ. For any concentration that is high enough
to give shear banding, the flow curve shows the usual non-analytic kink at the onset of banding, followed by a coexistence
“plateau” that slopes upwards, dΣ/dˉ > 0. As the concentration is reduced, the width of the coexistence regime diminishes
and eventually terminates at a non-equilibrium critical point [Σc,ˉφc,ˉc]. We outline the way in which the flow phase diagram can be reconstructed from a family of such flow curves, Σ(ˉ,ˉφ), measured
for several different values of ˉφ. This reconstruction could be used to check new measurements of concentration differences
between the coexisting bands. Our d-JS-φ model contains two different spatial gradient terms that describe the interface between
the shear bands. The first is in the viscoelastic constitutive equation, with a characteristic (mesh) length l. The second is in the (generalised) Cahn-Hilliard equation, with the characteristic length ξ for equilibrium concentration-fluctuations.
We show that the phase diagrams (and so also the flow curves) depend on the ratio r ≡ l /ξ, with loss of unique state selection at r = 0. We also give results for the full shear-banded profiles, and study the divergence of the interfacial width (relative
to l and ξ) at the critical point.
Received: 20 December 2002 / Accepted: 24 April 2003 / Published online: 11 June 2003
RID="a"
ID="a"e-mail: physf@irc.leeds.ac.uk
RID="b"
ID="b"e-mail: p.d.olmsted@leeds.ac.uk 相似文献
58.
Electromigration of hydrogen in YH(3-delta) is studied by exploiting the H concentration dependence of the optical transmission of YH(3-delta). We find the effective valence Z* of H in YH(3-delta) to be negative. Its value is dominated by a huge wind-force-like term, i.e., Z* approximately K/rho, with K approximately -60 mOmega cm. This value is 3 orders of magnitude larger than typical for H in metals. In an Arrhenius plot, the ratio of hydrogen and electron fluxes extrapolates to unity at infinite temperature, suggesting a one-to-one correlation of hydrogen and electron hopping. We discuss our results in the light of strong electron correlation theories which predict each proton to bind two electrons in a sort of Zhang-Rice singlet. 相似文献
59.
We study a simple model of shear banding in which the flow-induced phase is destabilized by coupling between flow and microstructure (wormlike micellar length). By varying the strength of instability and the applied shear rate, we find a rich variety of oscillatory and chaotic shear banded flows. At low shear and weak instability, the induced phase pulsates next to one wall of the flow cell. For stronger instability, high shear pulses ricochet across the cell. At high shear we see oscillating bands on either side of central defects. We discuss our results in the context of recent experiments. 相似文献
60.
The Abel inversion, used to reconstruct axisymmetric radial profiles from line-of-sight intensity measurements, is increasingly used to make spatially resolved combustion measurements. An Abel deconvolution is valid only when incoming rays are parallel, whereas most practical optical setups used for emission imaging consist of single-lens and multilens systems that collect light in a cone, over a nonzero solid angle. A ray-tracing simulation was performed to aid in understanding how optical collection geometry affects measured intensity signals and the resultant reconstructed emissivity profiles. Simulation results are compared with emission tomography measurements performed on an axisymmetric laminar diffusion flame. 相似文献