Creating Excess Electrons at the Anatase TiO2(101) Surface

Excess electrons facilitate redox reactions at the technologically relevant anatase TiO₂(101) surface. The availability of these electrons is related to the defect concentration at the surface. We present two-photon (2PPE, 3.10–3.54 eV) and ultraviolet (UPS, 21.2 & 40.8 eV) photoemission spectroscopy measurements evidencing an increased concentration of excess electrons following electron bombardment at room temperature. Irradiation-induced surface oxygen vacancies are known to migrate into the sub-surface at this temperature, quickly equilibrating the surface defect concentration. Hence, we propose that the irradiated surface is hydroxylated. Peaks in UPS difference spectra are observed centred 8.45, 6.50 and 0.73 eV below the Fermi level, which are associated with the 3σ and 1π hydroxyl molecular orbitals and Ti 3d band gap states, respectively. The higher concentration of excess electrons at the hydroxylated anatase (101) surface may increase the potential for redox reactions.

Development of a new photoelectron spectroscopy instrument combining an electrospray ion source and photoelectron imaging

A new apparatus has been constructed that combines electrospray ionization with a quadrupole mass filter, hexapole ion trap, and velocity-map imaging. The purpose is to record photoelectron images of isolated chromophore anions. To demonstrate the capability of our instrument we have recorded the photodetachment spectra of isolated deprotonated phenol and indole anions. To our knowledge, this is the first time that the photodetachment energy of the deprotonated indole anion has been recorded.

RYDBERG WAVEPACKETS IN MOLECULES: From Observation to Control

▪ Abstract  Significant advances in laser technology have led to an increasing interest in the time evolution of Rydberg wavepackets as a means to understanding, and ultimately controlling, quantum phenomena. Rydberg wavepackets in molecules are particularly interesting as they possess many of the dynamical complications of large molecules, such as nonadiabatic coupling between the various degrees of freedom, yet they remain tractable experimentally and theoretically. This review explains in detail how the method of interfering wavepackets can be applied to observe and control Rydberg wavepackets in molecules; it discusses the achievements to date and the possibilities for the future.

Femtosecond lasers in gas phase chemistry

This critical review is intended to provide an overview of the state-of-the-art in femtosecond laser technology and recent applications in ultrafast gas phase chemical dynamics. Although "femtochemistry" is not a new subject, there have been some tremendous advances in experimental techniques during the last few years. Time-resolved photoelectron spectroscopy and ultrafast electron diffraction have enabled us to observe molecular dynamics through a wider window. Attosecond laser sources, which have so far only been exploited in atomic physics, have the potential to probe chemical dynamics on an even faster timescale and observe the motions of electrons. Huge progress in pulse shaping and pulse characterisation methodology is paving the way for exciting new advances in the field of coherent control.

Optical control of the rotational angular momentum of a molecular Rydberg wave packet

An intuitive scheme for controlling the rotational quantum state of a Rydberg molecule is demonstrated experimentally. We determine the accumulated phase difference between the various components of a molecular electron wave packet, and then employ a sequence of phase-locked optical pulses to selectively enhance or depopulate specific rotational states. The angular momentum composition of the resulting wave packet, and the efficiency of the control scheme, is determined by calculating the multipulse response of the time-dependent Rydberg populations.

Controlling the angular momentum composition of a Rydberg electron wave packet

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.

The dynamics of Rydberg electron wavepackets in NO

Rydberg electron wavepackets have been studied in molecular NO for a variety of rotational states of the ion core. Predominantly radial motion of the electron wavepacket is observed which is similar to that previously reported in atomic systems. Interference effects similar to those observed in unperturbed Rydberg series are evident and third and fourth order partial revivals are identified. Most interestingly, when the classical period of electronic motion is close to the classical period of rotation of the molecular ion, the molecular dynamics dominates the electronic dynamics.