Transition state in atomic physics

The transition state is fundamental to modern theories of reaction dynamics: essentially, the transition state is a structure in phase space that all reactive trajectories must cross. While transition-state theory (TST) has been used mainly in chemical physics, it is possible to apply the theory to considerable advantage in any collision problem that involves some form of reaction. Of special interest are systems in which chaotic scattering or half-scattering occurs such as the ionization of Rydberg atoms in external fields. In this paper the ionization dynamics of a hydrogen atom in crossed electric and magnetic fields are shown to possess a transition state: We compute the periodic orbit dividing surface (PODS) which is found not to be a dividing surface when projected into configuration space. Although the possibility of a PODS occurring in phase space rather than configuration space has been recognized before, to our knowledge this is the first actual example: its origin is traced directly to the presence of velocity-dependent terms in the Hamiltonian. Our findings establish TST as the method of choice for understanding ionization of Rydberg atoms in the presence of velocity-dependent forces. To demonstrate this TST is used to (i) uncover a multiple-scattering mechanism for ionization and (ii) compute ionization rates. In the process we also develop a method of computing surfaces of section that uses periodic orbits to define the surface, and examine the fractal nature of the dynamics

Statistical Theory of Asteroid Escape Rates

Transition states in phase space are identified and shown to regulate the rate of escape of asteroids temporarily captured in circumplanetary orbits. The transition states, similar to those occurring in chemical reaction dynamics, are then used to develop a statistical semianalytical theory for the rate of escape of asteroids temporarily captured by Mars. Theory and numerical simulations are found to agree to better than 1%. These calculations suggest that further development of transition state theory in celestial mechanics, as an alternative to large-scale numerical simulations, will be a fruitful approach to mass transport calculations

Fractal Weyl law behavior in an open, chaotic Hamiltonian system

We numerically show fractal Weyl law behavior in an open Hamiltonian system that is described by a smooth potential and which supports numerous above-barrier resonances. This behavior holds even relatively far away from the classical limit. The complex resonance wave functions are found to be localized on the fractal classical repeller.Comment: 4 pages, 3 figures. to appear in Phys Rev

A brief CBT intervention for depersonalisation-derealisation disorder in psychosis: Results from a feasibility randomised controlled trial

Background and objectives: Depersonalisation/derealisation symptoms are prevalent in psychosis patients, are associated with increased impairment, and may maintain psychosis symptoms. We aimed to establish the feasibility and acceptability of a brief, six session therapy protocol adapted from a Cognitive-Behavioural model of Depersonalisation-Derealisation Disorder (DDD) in participants with psychotic symptoms. // Methods: A single-blind, randomised controlled trial was conducted with a treatment-as-usual control condition. Feasibility and acceptability estimates included rates of referral, acceptance, eligibility, consent, satisfaction and improved skills/knowledge to manage depersonalisation. // Results: Twenty-one individuals were recruited to the trial. Results suggest that the intervention was feasible and acceptable to participants and there is some signal of effect on clinical outcomes. // Limitations: There were some challenges in recruitment. Recruitment feasibility estimates from the research register used may not be informative for future trials recruiting directly from teams. // Conclusions: Overall, the results suggest that further investigations would be of interest and recommendations for this are made

The Infrared Spectrum of the He-C2D2 Complex

Spectra of the helium-acetylene complex are elusive because this weakly bound system lies close to the free rotor limit. Previously, limited assignments of He–C2D2 transitions in the R(0) region of the ν3 fundamental band (≈2440 cm−1) were published. Here, new He–C2D2 infrared spectra of this band are obtained using a tunable optical parametric oscillator laser source to probe a pulsed supersonic slit jet expansion from a cooled nozzle, and the analysis is extended to the weaker and more difficult P(1) and R(1) regions. A term value approach is used to obtain a consistent set of “experimental” energy levels. These are compared directly with calculations using two recently reported ab initio intermolecular potential energy surfaces, which exhibit small but significant differences. Rovibrational energies for the He–C2H2 complex are also calculated using bothsurfaces. A Coriolis model, useful for predicting spectral intensities, is used to interpret the energy level patterns, and a comparison with the isoelectronic complex He–CO is made