Radical Role Reversal

LE13164

- It is an elementary principle of chemistry that radicals, i.e. atoms or molecules with an unpaired electron orbiting their nucleus, are highly reactive, while closed-shell species, i.e. atoms and molecules where the electrons are all paired, are relatively stable. In this paper, atoms and ions are produced and confined at ultracold temperatures in a novel hybrid trap, dubbed the MOTION trap. By carefully monitoring the interaction of the ultracold atoms and ions in this trap, it is observed that at these ultracold temperatures closed-shell species can in fact be thousands of times more reactive than radicals. This role-reversal is found to be the consequence of the underlying quantum dynamics driving the chemical reaction, which are normally obscured at room temperature. Given that reactions of the type observed in this work are important for determining astrophysical processes and in planned hybrid atom-ion devices, this work highlights both the need for a renewed effort in laboratory astrophysics and fully-quantum chemical reaction calculations on a case-by-case basis to guide the next generation of atom-ion device design.

How hard is it to generate a complex birdsong?

EH10901

- Behavior emerges from the interaction between a nervous system and a peripheral bio-mechanical device executing those instructions. In that perspective, how much of the complexity is coded in the driving commands, and how much emerges in the physical device? In this work we study the acoustically challenging song the Zebra finch, and test the hypothesis that much of its acoustic complexity is due to the nonlinear nature of the avian vocal organ. We test it by reconstructing the parameters of a simple model, and comparing those results with direct measurements of the physiological parameters driving the vocal organ. Simple instructions, driving the nonlinear device, generate the most peculiar and acoustically rich song of the Zebra finch.

High-brightness multi-wavelength remote laser for detecting multiple hazard gases in air

LE13721AR

- Since the first ruby laser was demonstrated in 1960, there have been enormous requirements for a variety of coherent light sources in a broad spectrum of fields covering science and engineering. In environmental science, there has been a large amount of research effort aiming at measuring atmospheric trace species over a long distance. The ability to control the generation of coherent light source with different frequencies at a designed location would provide a new strategy to meet the pressing needs of various environmental issues from monitoring global warming and stratospheric ozone depletion to early detection of nuclear reactor radiation leak and biological treat agents in air. To date, a multi-wavelength remote laser in air that allows for dynamically switching the operating wavelength has not yet been achieved, although this type of laser is certainly of high importance for detecting multiple hazard gases. Here, we demonstrate a harmonic-seeded switchable multi-wavelength laser in air driven by intense mid-infrared femtosecond laser pulses. Furthermore, population inversion in the multi-wavelength remote laser occurs at an unexpected ultrafast time-scale (i.e., less than ~200 fs) owing to direct formation of excited molecular nitrogen ions by strong-field ionization of inner-valence electrons. The bright multi-wavelength laser in air opens the perspective for remote detection of multiple pollutants based on nonlinear spectroscopy.

New way to pack marbles and buckyballs

LJ12785ER


- Spherical objects inside a cylinder can now be packed more efficiently than ever. With a suitable template, the densest packings can surprisingly be obtained from a very simple deposition procedure. The findings will have a broad range of applications in physics, from the macro- to the nano-scale, and also in commercial packaging.