Deuterium fractionation in interstellar molecules is used to trace both the origins of objects and the physical conditions in the interstellar medium. The main route of formation of deuterated methanol is believed to be successive hydrogenation of CO and subsequent H-D exchange. However, O(¹D) insertion is a known, barrierless pathway of methanol formation both on ices and in the gas phase that may contribute to the population of deuterated species observed in the ISM. There are currently no experimental or theoretical studies on whether O(¹D) preferentially inserts into C-H or C-D bonds. As such, O(¹D) insertion and O(³P) (a side product from photolysis of O(¹D) precursors) hydrogen abstraction are investigated for their reactions with CH₄ and CH₃D using CCSD(T)/cc-pCVTZ. The kinetics of the reaction pathways are investigated under ISM relevant temperature and pressure conditions using the Master Equation Solver for Multi-Energy Well Reactions (MESMER). Here we present the results of these studies, including the reaction coordinate, theoretical kinetic rate constants, branching ratios, and predicted kinetic isotope effects of these reaction pathways.

Radicals are important reactants and products of gas phase reactions in atmospheric, combustion, and astrophysical environments. Many experimental techniques have been used to observe radicals from kinetic reactors, with the use of rotational spectroscopy growing in this role during the last decade. A fast flow tube reactor has recently been combined with chirped pulse Fourier transform millimeter wave spectroscopy for the dual purpose of observing product branching ratios from reactions and selectively producing radicals for spectroscopy. Radicals are produced in the well characterized laminar flow of the fast flow tube using a microwave discharge of F₂, where free F atoms can then abstract hydrogen from -CH bonds. The products of reactions can then be monitored using a mass spectrometer and millimeter wave spectroscopy. Design of apparatus and proof of principle studies of the O₂+ CH₂OHreaction and its products will be discussed.

Clusters and related (sub)-nanoscale systems are promising alternatives to traditional bulk materials as they often exhibit novel properties, stemming from their quantized sizes, that can be developed for energy conversion applications. I will present our recent ultrafast spectroscopy measurements that demonstrate the exquisite tunability of the physical and chemical properties of clusters, through systematic adjustment of their atomic composition and size, enables new understandings to control energy flow. The excited state lifetimes of neutral metal oxide clusters up to ~1 nm in diameter in size are systematically measured with femtosecond time-resolved mass spectrometry. Distinct transitions in excited state relaxation behaviors and associated calculated charge carrier distributions are recorded in several systems as the clusters grow, marking a distinct fundamental change in their properties with size. By tuning the electron density of neutral metal oxides clusters with atomic precision, our ultrafast measurements act as a window to monitor electron correlation and identify the structural features driving carrier localization/separation, polaron formation and development of Rydberg excitons.$^{1–3}$ Our innovative approach has also proven beneficial for identifying the onset of metallic behavior in pure metal clusters.$^{4}$ The electronic relaxation properties are strongly dependent on both size and local structure, enabling sub-nanometer clusters to exhibit metallic or semiconducting properties, and even transition between the two in direct relation to time-dependent density functional theory calculations of the topological parameters and charge carrier delocalization character of the photoexcitation. 1 Garcia, Shaffer and Sayres, Ultrafast pump–probe spectroscopy of Neutral Fe$_{n}$O$_{m}$ Clusters (n,m $\leq$ 16), PCCP, 2020, 22, 24624–24632. 2 Garcia, Heald, Shaffer and Sayres, Oscillation in Excited State Lifetimes with Size of Sub-nanometer Neutral (TiO$_{2}$)$_{n}$ Clusters Observed with Ultrafast Pump–Probe Spectroscopy, JPCL, 2021, 12, 4098–4103. 3 Rotteger, Jarman, Sobol, Sutton and Sayres, Sub-picosecond Dynamics of Rydberg Excitons Produced from Ultraviolet Excitation of Neutral Cuprite (Cu$_{2}$O)$_{n}$ Clusters, n$\leq$13, https://doi.org/10.26434/chemrxiv-2024-9cr26. 4 Rotteger, Jarman, Sutton and Sayres, Size Onset of Metallic Behavior in Neutral Aluminum Clusters, https://doi.org/10.26434/chemrxiv-2024-9dtb7

Flows over hypersonic vehicles result in high peak temperatures sufficient for generation of plasmas, leading to communications blackout and UV emission signatures. One of the key ionization processes behind strong shock waves produced in hypersonic flight is associative ionization in collisions of atoms, generated during dissociation of molecular nitrogen and oxygen, including excited atoms. The objective of the present work is to generate N and O atoms, both in their ground electronic states, N(⁴S) and O(³P) and excited metastable states, N^*(²D,²P) and O^*(¹D,¹S), in a laboratory experiment, and to study their associative ionization generating N₂⁺ and NO⁺ ions. A heated plasma flow reactor is used to generate a stable and diffuse plasma over a wide range of temperatures, T = 300-1500 K, and pressures ranging from a few tens to a few hundred Torr, using high peak voltage (20-30 kV), ns duration discharge pulses (10-100 ns). Time-resolved measurements of N₂⁺ ions in the discharge afterglow by the pulsed UV Cavity Ring Down Spectroscopy (CRDS) near 391 nm exhibit a multi-exponential ring down decay, due to the variation of the ion number density over time. The ring down traces are also affected by the laser linewidth, which is comparable to the absorption linewidth. This effect is accounted for during the CRDS data reduction. The N₂⁺ number density in the afterglow shows a transient rise with a subsequent decay, indicating the effect of associative ionization of excited species accumulated during the discharge burst. Comparison of N₂⁺ and excited metastable N₂(A³Σ_u⁺) molecules, measured by Tunable Diode Laser Absorption Spectroscopy, suggests that the excited species resulting in the associative ionization are the metastable N atoms generated during the N₂(A) quenching by the ground state nitrogen atoms. Ongoing work is focused on the measurements of NO⁺ ions by mid-infrared, cw Cavity Ring Down Spectroscopy, as well as on the direct measurements of the excited atoms by the vacuum UV absorption spectroscopy.

Matrix-assisted laser desorption/ionization (MALDI) is a widely used mass spectrometric tool in analyzing biologically relevant molecules. Although MALDI was invented more than three decades ago, the primary ion formation process remains poorly understood. Several models have been proposed to explain the mechanism of MALDI. However, to date, the exciton pooling model proposed by Knochenmuss has been shown to agree with various experimental observations. Fluorescence spectroscopy was the method used in previous studies to confirm the exciton pooling model. Even though fluorescence spectroscopy provides information about the lifetime and mobility of the excitons, it does not yield direct information about the reaction in which the excitons are involved. Furthermore, a lack of comprehensive understanding of matrix band structures and work functions makes the basis of the coupled chemical and physical dynamics (CPCD) model questionable. Here we will show that 3D momentum electron imaging and two-photon photoemission spectroscopy can be used to extract the detailed electronic properties and exciton lifetime. Preliminary results suggested that primary ion formation in UV-MALDI on 2,5 dihydroxybenzoic acid didn’t show any evidence of exciton pooling mechanism. Further investigation will need to be carried out to determine the specific reaction mechanism that occurs leading to the formation of primary ions. The results of this study will provide a broader understanding of primary ionization in the MALDI process.

Nitrogen-substituted polycyclic aromatic hydrocarbons (NPAHs) are ubiquitous in the universe and fundamental components of vital biomolecules such as DNA and RNA, and are incorporated into proteins via amino acids tryptophan and pyrrolysine. However, routes to their formation in the interstellar medium have remained largely elusive. Here, we report an unconventional low-temperature synthesis of the simplest prototype of NPAHs — indole (c-C₈H₇N) — along with its component cyclic building blocks, pyrrole (c-C₄H₅N) and aniline (c-C₆H₅NH₂), in model interstellar ices composed of acetylene (C₂H₂) and ammonia (NH₃) upon exposure to simulated galactic cosmic ray (GCRs) irradiation. Isomer-selective resonance-enhanced multiphoton ionization (REMPI) and tunable single-photon photoionization reflectron time-of-flight mass spectrometry (REMPI/PI-ReToF-MS) were used to detect indole, pyrrole, and aniline. Experimental conditions simulate those found in a dense interstellar molecular cloud during star-formation and gravitational collapse which suggest that these heteroaromatics represent worthwhile astronomical targets for future astronomical searches. The combination of laboratory experiments with electronic structure calculations reveals critical insights into the radical reaction pathways of NPAHs and their precursors, thus bringing us closer to an understanding of the formation of a class of molecules that are central to the development and continuation of life.

Non-equilibrium internal state distributions have been observed in molecules undergoing evaporation or sublimation from the condensed phase [1-5]. These studies have largely been focused on diatomic or triatomic species that can be examined by laser-based probes such as LIF or IR absorption. With the capabilities of CPICE (Chirped Pulse ICE) we extend these studies to polyatomic systems desorbing from an ice surface applying detection by broadband rotational spectroscopy. Here we examine iso-propyl cyanide which contains several low frequency vibrational modes that permit measurement of the nascent vibrational temperature of molecules that have undergone sublimation. Our results indicate that the two lowest lying modes of i-PrCN (ν30=1 and ν29=1) yield distinct vibrational temperatures which are colder than the temperature at which it desorbs. 1. David J. Nesbitt, Alex M. Zolot, Joseph R. Roscioli, and Mikhail Ryazanov, Acc. Chem. Res. (2023): 56, 6, 700-711 2. Miles J. Weida, Jenette M. Sperhac, and David J. Nesbitt, J. Chem Phys. (1996): 105, 749-766 3. D.F. Padowitz and S.J. Sibener, Surface Science. (1989): 217, 233-246 4. Michelle R. Brann, Stephen P. Hansknecht, Xinyou Ma, and S.J. Sibener, J. Phys. Chem. A. (2021): 125, 9405-9413 5. William A. Alexander, Jianming Zhang, Vanessa J. Murray, Gilbert M. Nathanson, and Timothy K. Minton, Faraday Discuss. (2012): 157, 355-374

Plasmonic nanomaterials such as noble metal-based particles exhibit excellent energy harvesting capabilities due to the extraordinary light-matter interaction. The larger optical absorption cross-sections of metallic nanoparticles compared to small molecules with the equivalent volumes enable highly sensitive imaging and spectroscopic measurements on single particle level. Over the past decade, various technologies have been proposed to realize absorption spectroscopy including photothermal spectroscopy which takes advantage of the photo-to-thermal conversion via non-radiative decay of a particle and modulates the refractive index fluctuations of the surrounding media to quantify absorption signals. In this talk, I will introduce a photothermal absorption spectroscopy setup based on a transmission-mode photothermal heterodyne imaging system integrated with a white laser, and demonstrate its implications in the measurements of spectroscopic signatures. Furthermore, I will enumerate our recent work on measuring plasmon-induced charge transfer between metal and metal-oxide heterogeneous interface by correlating absorption and scattering spectroscopy. The high energetic electrons during plasmon dephasing injecting from gold to the adjacent semiconductor produces reduced plasmon decay lifetime while broadens spectral linewidth in both radiative and non-radiative decay pathways.

The process of purifying monoclonal antibodies using chromatography represents a significant expense in the pharmaceutical sector, primarily due to the low throughput caused by antibody aggregation at high concentrations. This aggregation hampers the efficiency of separations. A key gap in our understanding is how the orientation of antibodies influences their aggregation behavior at these high concentrations. In response, we propose the development of a novel optical microscope designed to observe the spatial and orientational dynamics of antibodies at the interfaces of chromatography. Our findings showcase the microscope's capability to accurately determine the 3D positions and orientations of antibodies using cutting-edge phase modulation techniques. By allowing for precise monitoring of how antibodies interact with both the substrate and each other, this technology promises to deepen our comprehension of antibody aggregation mechanisms. Such knowledge is poised to refine purification strategies and enhance the reliability of antibody separations. Ultimately, this advancement could lead to more cost-effective manufacturing processes in the pharmaceutical industry.

Stimuli-responsive materials have attracted considerable attention due to their ability to react to external triggers. Plasmonic nanohybrids incorporating both gold nanoparticles and stimuli-responsive materials can enable the active control of plasmonic properties such as resonance tuning, charge transfer, and plasmon energy transfer. However, the broad application of plasmonic nanohybrids requires a deep understanding of the underlying mechanisms that govern their active control and responsiveness. In this work, we report the effect of polymer conformational changes on the localized surface plasmon resonance (LSPR) of single hybrid nanostructures consists of poly(N-isopropylacrylamide) (pNIPAM) encapsulated gold nanoparticles (AuNPs). To achieve this objective, single-particle dark-field hyperspectral imaging was used for the real-time monitoring of stimuli-modulated hybrid nanoelectrode charging via changes in the plasmon resonance. Upon changes in temperature, the resonance energy and scattering intensity show responses that are both dynamic and reversible, thus demonstrated the active control of plasmonic properties at the nanoscale. Furthermore, our single-particle approach uncovered internal heterogeneity of the plasmonic nanohybrids, which shows great promise in the understanding of structural-spectral relationship that traditional ensemble techniques are unable to discern. In conclusion, this work provides an understanding of the influence of the plasmonic core on polymer collapse dynamics, thereby enabling the rational design of flexible and easily processable devices and architectures.