Regular threshold-energy increase with charge for neutral-particle emission in collisions of electrons with oligonucleotide anions

On the Thermal Behavior during Spatial Anisotropic Femtoseconds Laser-DNA Interaction: The Crucial Role of Hermite Polynomials

A novel analytical formalism based on the quantum heat transport equation is proposed for the interaction of fs-laser pulses with deoxyribonucleic acid (DNA) strands. The formalism has the intensity of the laser beam and the interaction time between the laser and the DNA as input parameters. To this end, the thermal distribution generated in the irradiated DNA strands was introduced by splitting the laser beam into transverse Hermite-Gauss modes. To achieve this goal, a new powerful mathematical model was developed and applied. Fluctuations in laser intensity were taken into account by modeling them as superpositions of Hermite-Gauss laser modes. These analyses were carried out for a laser pulse duration of 100 fs, where a tiny heat-affected zone is expected, with positive predicted effects on the stability and repeatability of this technology. The main conclusion is that the laser beam spatial distribution intensity plays an essential role in the generation of the shape and magnitude of the thermal field at the junction of the irradiated DNA strands. The model may prove useful in modeling laser beam processing under significant intensity fluctuations. There are at least two main areas of application for the present model of heat transfer from laser to DNA: (i) the study of DNA elongation without destroying the target information (for a sample temperature variation lower than 10 K; in the case of H[1,y]); and (ii) cancer treatment (especially of skin tissue), where we should obtain a temperature variation higher than 10 K (but lower than 30 K; in the case of H[2,y], H[4,y]), in order to eradicate the diseased cells.

Analysis of ionic photofragments stored in an electrostatic storage ring

A new method to analyze the properties of fragment ions created in storage ring experiments is presented. The technique relies on an acceleration of ionic fragments immediately after production whereby the fragments are stored in the storage ring. To obtain a fragment mass spectrum, the storage ring is exploited as an electrostatic analyzer (ESA) in which case the number of stored fragment ions is recorded as a function of the applied acceleration potential. However, the storage ring can additionally be employed as a time-of-flight (TOF) instrument by registering the temporal distribution of fragment ions. It is demonstrated that the combined ESA-TOF operation of the ring allows not only to determine fragment masses with much better resolution compared to the ESA mode alone but also enables the extraction of detailed information on the fragmentation dynamics. The method is described analytically and verified with photodissociation experiments on stored Cl2 (-) at an excitation wavelength of 530 nm.

When electrons meet molecular ions and what happens next: dissociative recombination from interstellar molecular clouds to internal combustion engines

The interaction of matter with its environment is the driving force behind the evolution of 99% of the observed matter in the universe. The majority of the visible universe exists in a state of weak ionization, the so called fourth state of matter: plasma. Plasmas are ubiquitous, from those occurring naturally; interstellar molecular clouds, cometary comae, circumstellar shells, to those which are anthropic in origin; flames, combustion engines and fusion reactors. The evolution of these plasmas is driven by the interaction of the plasma constituents, the ions, and the electrons. One of the most important subsets of these reactions is electron-molecular ion recombination. This process is significant for two very important reasons. It is an ionization reducing reaction, removing two ionised species and producing neutral products. Furthermore, these products may themselves be reactive radical species which can then further drive the evolution of the plasma. The rate at which the electron reacts with the ion depends on many parameters, for examples the collision energy, the internal energy of the ion, and the structure of the ion itself. Measuring these properties together with the manner in which the system breaks up is therefore critical if the evolution of the environment is to be understood at all. Several techniques have been developed to study just such reactions to obtain the necessary information on the parameters. In this paper the focus will be on one the most recently developed of these, the Ion Storage Ring, together with the detection tools and techniques used to extract the necessary information from the reaction.

A "tabletop" electrostatic ion storage ring: Mini-Ring

We report on the design, construction, and commissioning of a novel electrostatic ion storage ring of small dimensions--in the following referred to as "Mini-Ring." Mini-Ring consists of four horizontal parallel-plate deflectors and two conical electrostatic mirrors. Ions are injected through the two deflectors on the injection side and off axis with respect to the conical mirrors which face each other. The first injection deflector, originally at zero voltage, is switched to its set value such that the ions after one turn follow stable trajectories of lengths of roughly 30 cm. This design reduces the number of electrodes necessary to guide the ion beam through the ring in stable orbits. The six elements (deflectors and mirrors) are placed on a common grounded plate--the tabletop. Here, we present the design, ion trajectory simulations, and results of the first test experiments demonstrating the successful room-temperature operation of Mini-Ring at background pressures of 10(-6) - 10(-7) mbar.

A new technique for time-resolved daughter ion mass spectrometry on the microsecond to millisecond time scale using an electrostatic ion storage ring

A new method for time-resolved daughter ion mass spectrometry is presented, based on the electrostatic ion storage ring in Aarhus, ELISA. Ions with high internal energy, e.g., as a result of photoexcitation, dissociate and the yield of neutrals is monitored as a function of time. This gives information on lifetimes in the microsecond to millisecond time range but no information on the fragment masses. To determine the dissociation channels, we have introduced pulsed supplies with switching times of a few microseconds. This allows rapid switching from storage of parent ions to storage of daughter ions, which are dumped into a detector after a number of revolutions in the ring. A fragment mass spectrum is obtained by monitoring the daughter ion signal as a function of the ring voltages. This technique allows identification of the dissociation channels and determination of the time dependent competition between these channels.