We present work detailing the destruction of the nerve agent simulant diisopropyl methylphosphonate (DIMP) via rapid laser heating under atmospheric conditions. Following Nd:YAG laser ablation of liquid DIMP deposited on a graphite substrate, both parent and product fragments are transmitted via capillary from an atmospheric chamber to a vacuum chamber containing a high-resolution mass spectrometer. This allows for real-time measurements of product distributions under a variety of temperature and atmospheric conditions. Ex situ Fourier transform infrared (FTIR) spectroscopy analysis of the same chamber contents provides complementary information about product identities and fragmentation pathways. Results demonstrate that product distributions depend on heating rate, surface temperature, and atmospheric oxygen content. In the destruction of the DIMP, the relative yields of alkene products depends significantly on laser power; smaller products are relatively more abundant at higher ablation temperatures. We also show that in the absence of atmospheric oxygen, the concentration of oxygenated products decreases sharply relative to alkene and alkane products. This suggests that under high-temperature conditions, atmospheric oxygen is incorporated directly into the products of the fragmented simulant. This project extends significantly our understanding of the fundamental chemistry of these dangerous compounds under atmospheric and rapidly changing thermal conditions. The results have critical implications for the development of effective chemical warfare agent decontamination and destruction strategies.

We present research detailing the sticking probability of CH4 on various D2O ices of terrestrial and astrophysical interest using a combination of time-resolved, in situ reflection absorption infrared spectroscopy (RAIRS) and King and Wells mass spectrometry techniques. As the incident translational energy of CH4 increases (up to 1.8 eV), the sticking probability decreases for all ice films studied, which include high-density, non-porous amorphous (np-ASW), and crystalline (CI) films as well as porous amorphous (p-ASW) films with various pore morphologies. Importantly, sticking probabilities for all p-ASW films diverge and remain higher than either np-ASW or CI films at the highest translational energies studied. This trend is consistent across all porous morphologies studied and does not depend on pore size or orientation relative to the substrate. It is proposed that in addition to offering slightly higher binding energies the porous network in the D2O film is very efficient at dissipating the energy of the incident CH4 molecule. These results offer a clear picture of the initial adsorption of small molecules on various icy interfaces; a quantitative understanding of these mechanisms is essential for the accurate modeling of many astrophysical processes occurring on the surface of icy dust particles.

Abstract. In microbiology research, there is a strong need for next-generation imaging and sensing instrumentation that will enable minimally invasive and label-free investigation of soft, hydrated structures, such as in bacterial biofilms. White-light interferometry (WLI) can provide high-resolution images of surface topology without the use of fluorescent labels but is not typically used to image biofilms because there is insufficient refractive index contrast to induce reflection from the biofilm's interface. The soft structure and water-like bulk properties of hydrated biofilms make them difficult to characterize in situ, especially in a nondestructive manner. We build on our prior description of static biofilm imaging and describe the design of a dynamic growth flow cell that enables monitoring of the thickness and topology of live biofilms over time using a WLI microscope. The microfluidic system is designed to grow biofilms in dynamic conditions and to create a reflective interface on the surface while minimizing disruption of fragile structures. The imaging cell was also designed to accommodate limitations imposed by the depth of focus of the microscope's objective lens. Example images of live biofilm samples are shown to illustrate the ability of the flow cell and WLI instrument to (1) support bacterial growth and biofilm development, (2) image biofilm structure that reflects growth in flow conditions, and (3) monitor biofilm development over time nondestructively. In future work, the apparatus described here will enable surface metrology measurements (roughness, surface area, etc.) of biofilms and may be used to observe changes in biofilm structure in response to changes in environmental conditions (e.g., flow velocity, availability of nutrients, and presence of biocides). This development will open opportunities for the use of WLI in bioimaging. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

We examine the initial differential sticking probability of CH 4 and CD 4 on CH 4 and CD 4 ices under nonequilibrium flow conditions using a combination of experimental methods and numerical simulations. The experimental methods include time-resolved in situ reflection–absorption infrared spectroscopy (RAIRS) for monitoring on-surface gaseous condensation and complementary King and Wells mass spectrometry techniques for monitoring sticking probabilities that provide confirmatory results via a second independent measurement method. Seeded supersonic beams are employed so that the entrained CH 4 and CD 4 have the same incident velocity but different kinetic energies and momenta. We found that as the incident velocity of CH 4 and CD 4 increases, the sticking probabilities for both molecules on a CH 4 condensed film decrease systematically, but that preferential sticking and condensation occur for CD 4 . These observations differ when condensed CD 4 is used as the target interface, indicating that the film’s phonon and rovibrational densities of states, and collisional energy transfer cross sections, have a role in differential energy accommodation between isotopically substituted incident species. Lastly, we employed a mixed incident supersonic beam composed of both CH 4 and CD 4 in a 3:1 ratio and measured the condensate composition as well as the sticking probability. When doing so, we see the same effect in the condensed mixed film, supporting an isotopic enrichment of the heavier isotope. We propose that enhanced multi-phonon interactions and inelastic cross sections between the incident CD 4 projectile and the CH 4 film allow for more efficacious gas–surface energy transfer. VENUS code MD simulations show the same sticking probability differences between isotopologues as observed in the gas–surface scattering experiments. Ongoing analyses of these trajectories will provide additional insights into energy and momentum transfer between the incident species and the interface. These results offer a new route for isotope enrichment via preferential condensation of heavier isotopes and isotopologues during gas–surface collisions under specifically selected substrate, gas-mixture, and incident velocity conditions. They also yield valuable insights into gaseous condensation under non-equilibrium conditions such as occur in aircraft flight in low-temperature environments. Moreover, these results can help to explain the increased abundance of deuterium in solar system planets and can be incorporated into astrophysical models of interstellar icy dust grain surface processes.

There is a need for imaging and sensing instrumentation that can monitor transitions in a biofilm structure in order to better understand biofilm development and emergent properties such as anti-microbial resistance. Herein, we describe the design, manufacture, and use of a microfluidic flow cell to visualize the surface structure of bacterial biofilms with white-light interferometry (WLI). The novel imaging chip enabled the use of this non-disruptive imaging method for the capture of high resolution three-dimensional profile images of biofilm growth over time. The fine axial resolution (3 nm) and the wide field of view (>1 mm by 1 mm) enabled the detection of biofilm formation as early as 3 h after inoculation of the flow cell with a live bacterial culture (). WLI imaging facilitated the monitoring of the early stages of biofilm development and subtle variations in the structure of mature biofilms. Minimally-invasive imaging enabled the monitoring of biofilm structure with surface metrology metrics (e.g., surface roughness). The system was used to observe a transition in the biofilm structure that occurred in response to exposure to a common antiseptic. In the future, WLI and the biofilm imaging cell described herein may be used to test the effectiveness of biofilm-specific therapies to combat common diseases associated with biofilm formation such as cystic fibrosis and periodontitis.