Listening to ultrasound from plants reveals xylem vessel anatomy. Ultrasound characterization of plant vessels.

Although it is well known that plants emit ultrasound bursts under drought stress, the exact origin of the acoustic waveform of these pulses has remained elusive. Here we present evidence for a correlation between the ultrasound spectrum of these pulses and the dimensions of the plant’s xylem vessels. Using a model that relates the vibrational excitations of the vessels to their geometric and viscoelastic properties, we develop a methodology to extract the internal xylem vessel dimensions from recorded ultrasound waveforms. We apply the method to ultrasound pulses from drying shoots of three vascular dicot plant species, and validate it by comparison with destructive measurements via microscopy. Our method demonstrates the potential for continuous monitoring of the vascular anatomy of plants. The ultrasonic, non-invasive characterization of internal vessel dimensions can lead to breakthroughs in speed and accuracy in plant phenotyping and disease detection in agriculture.

Hot carrier multiplication in plasmonic photocatalysis

Light-induced hot carriers derived from the surface plasmons of metal nanostructures have been shown to be highly promising agents for photocatalysis. While both nonthermal and thermalized hot carriers can potentially contribute to this process, their specific role in any given chemical reaction has generally not been identified. Here, we report the observation that the H2–D2 exchange reaction photocatalyzed by Cu nanoparticles is driven primarily by thermalized hot carriers. The external quantum yield shows an intriguing S-shaped intensity dependence and exceeds 100% for high light intensities, suggesting that hot carrier multiplication plays a role. A simplified model for the quantum yield of thermalized hot carriers reproduces the observed kinetic features of the reaction, validating our hypothesis of a thermalized hot carrier mechanism. A quantum mechanical study reveals that vibrational excitations of the surface Cu–H bond is the likely activation mechanism, further supporting the effectiveness of low-energy thermalized hot carriers in photocatalyzing this reaction.

Ramsauer–Townsend minimum in electron scattering from CF$$_4$$: modified effective range analysis

Elastic cross sections for electron scattering on tetrafluoromethane (CF$$_4$$ 4 ) from 0 up to 5 eV energy are analyzed using semi-analytical approach to the modified effective range theory (MERT). It is shown that energy and angular variations of differential, integral and momentum transfer cross sections can be parameterized accurately by six MERT coefficients up to the energy region of the resonant scattering. In particular, the model is used to determine the depth and the position of the Ramsauer–Townsend minimum as well as the s-wave scattering length. Moreover, we investigate the influence of the dipole polarizability value on the predictions of present model. To further validate our approach, the elastic data are combined with the Born-dipole cross sections for vibrational excitations as the input data for Monte Carlo simulation of electron swarm coefficients. Graphic Abstract

Vibrational resonant inelastic X-ray scattering in liquid acetic acid: a ruler for molecular chain lengths

Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O–H bond, the spectra lack the typical progression of vibrational excitations observed in RIXS spectra of comparable systems. We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding, which however cannot be observed in x-ray absorption but only by means of RIXS. This allows us to address the molecular structure of the liquid, and to determine a lower limit for the average molecular chain length.

The symmetric C-D stretching spectator mode in the H+CHD3→H2+CD3 reaction and its effect on dynamical modeling

The symmetric C-D stretching mode is a spectator mode in the H+CHD3→H2+CD3 reaction. Effects of multiple vibrational excitations of the CHD3 reactant are studied with the quantum transition-state (QTS) framework...

Quantum dynamics study of energy efficiency on reactivity for the OH + DBr reaction

For the OH + DBr reaction, we report a time-dependent, full dimensional, wave-packet calculation to examine the energy efficiency on reactivity. This study shows that the vibrational excitations of the...

A pair potential modeling study of F3− in neon matrices

First-principles investigations of the trifluoride anion in a neon environment reveal a small blue-shift of the fundamental vibrational excitations.

Vibrational Resonant Inelastic X-Ray Scattering Inliquid Acetic Acid: A Ruler for Molecular Chain Lengths

Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O-H bond, the spectra lack the typical progressionof vibrational excitations observed in RIXS spectra of comparable systems. We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding. This allows us to address the molecular structure of the liquid, and to determine a lower limit for the average molecular chain length.