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The reactions of He + with OCS and CO 2 have been studied at collision energies between ∼ k B ⋅ 200 mK and ∼ k B ⋅ 30 K by merging a beam of Rydberg He atoms with rotationally cold (∼3.5 K) seeded supersonic expansions containing either OCS or 13 CO 2 or a mixture of OCS (mole fraction 23.2%) and 13 CO 2 (76.8%). The observed product ions of the He + + 13 CO 2 and He + + OCS reactions are 13 CO + , and CS + and CO + , respectively. The He + + OCS capture rate coefficient increases by ∼75% with decreasing collision energy over the investigated range, whereas that of He + + 13 CO 2 decreases by ∼40%. The analysis of the experimental results using an adiabatic-channel capture model indicates that these opposite collision-energy dependences of the rate coefficients arise from the interaction between the charge of the ion and the electric multipole moments of OCS and 13 CO 2 . From the relative product-ion yields observed when using the mixture of OCS and 13 CO 2 , the He + + OCS collisions are inferred to be ∼20% more reactive than those between He + and 13 CO 2 . The comparison of the calculated thermal rate coefficients with earlier experiments suggests that about half of the He + + 13 CO 2 collisions are reactive.

The ion-molecule reactions He+ + CO → He + C+ + O and He+ + NO → He + N+ + O have been measured at collision energies between 0 and kB · 10 K. Strong variations of the rate coefficients are observed below kB · 5 K. The rate of the He+ + CO reaction decreases by ~30% whereas that of the He+ + NO reaction increases by a factor of ~1.5. These observations are interpreted in the realm of an adiabatic-channel capture model as arising from interactions between the ion charge and the dipole and quadrupole moments of CO and NO. We show that the different low-energy behavior of these reactions originates from the closed- vs. open-shell electronic structures of CO and NO., (Copyright 2023 Fernanda B. V. Martins, Valentina Zhelyazkova, Andreas Osterwalder, Frédéric Merkt. License: This work is licensed under a Creative Commons Attribution 4.0 International License.)

The reactions between ions and free radicals are among the fastest chemical reactions. They are predicted to proceed with large rates, even near 0 K, but so far, this prediction has not been verified experimentally. We report on measurements of the rate coefficient of the reaction between the ion He + and the free radical NO at collision energies in the range between 0 and ∼ k B ·10 K. To avoid heating of the ions by stray electric fields, the reaction is observed within the large orbit of a Rydberg electron of principal quantum number n ≥ 30, which shields the ion from external electric fields without affecting the reaction. Low collision energies are reached by merging a supersonic beam of He Rydberg atoms with a supersonic beam of NO molecules and adjusting their relative velocity using a chip-based Rydberg-Stark decelerator and deflector. We observe a strong enhancement of the reaction rate at collision energies below ∼ k B ·2 K. This enhancement is interpreted on the basis of adiabatic-channel capture-rate calculations as arising from the near-degenerate rotational levels of opposite parity resulting from the Λ-doubling in the X 2 Π 1/2 ground state of NO. With these new results, we examine the reliability of broadly used approximate analytic expressions for the thermal rate constants of ion-molecule reactions at low temperatures.

Recently, numerous studies report bats as reservoirs of emerging pathogens with little to no signs of infections. This is thought to be connected to the unique immune system of bats, which remains poorly characterized. Despite the physiological importance of the Neonatal Fc receptor (FcRn) in the homeostasis of IgG antibodies, it is unclear how its functional activity is evolutionary conservative among mammals, and so is the case for bats. Using surface plasmon resonance-based technology, we tested the interactions of IgG antibodies isolated from three bat species with recombinant human and mouse FcRn. Our data show that IgG from the studied bat species binds to both human and mouse FcRn, albeit with distinct affinities. Importantly, the binding pattern of bat IgG is similar to human IgG. This confirms the conservative nature of IgG-FcRn interaction and highlights the importance of FcRn IgG salvaging system in bats., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to declare., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Healthy wing membranes are essential for bats. They are critical for maintaining the water balance and, during hibernation, they protect the bat's body from dehydration. Assessing the state of the membrane visually is an easy and effective way to monitor a bat's health and discover abnormal structures and infections in wild bat populations. During pre- and post-hibernation surveys of bats' wings, we identified the presence of skin mites, Psorergatoideskerivoulae (Fain, 1959). The parasite causes cutaneous lesions on the wing membranes of the greater moused-eared bat, Myotismyotis (Borkhausen, 1797) and the lesser moused-eared bat, Myotisblythii (Tomes, 1857). The lesser mouse-eared bat is a new host for this parasite. Our study is the first to describe the histopathology of the infection on the wings of the greater and lesser mouse-eared bats. To our knowledge, this is the southernmost record of this parasite and the first mention of the genus Psorergatoides for the Balkans., (Nia Toshkova, Boyan Zlatkov, Albena Fakirova, Violeta Zhelyazkova, Nikolay Simov.)

We present experimental and theoretical studies of the He + + CH 4 and He + + CD 4 reactions at collision energies in the k B ·(0-10) K range. Helium atoms in a supersonic beam are excited to a low-field-seeking Rydberg-Stark state and merged with a supersonic beam of CH 4 or CD 4 using a curved surface-electrode deflector. The ion-molecule reactions are studied within the orbit of the helium Rydberg [He( n )] electron, which suppresses stray-electric-fields-induced heating and makes it possible to reach very low collision energies. The collision energy is varied by adjusting the velocity of the He( n ) atoms with the surface deflector, keeping the velocity of the methane beam constant. The reaction product ions (C(H/D) p + with p ∈ {1,2,3}) are collected in a time-of-flight mass spectrometer and monitored as a function of the collision energy. No significant energy-dependence of the total reaction yields of either reactions is observed. The measured relative reaction rate coefficient for the He + + CH 4 reaction is approximately twice higher than the one for the He + + CD 4 reaction. The CH + , CH 2 + and CH 3 + (CD + , CD 2 + and CD 3 + ) ions were detected in ratios 0.28(±0.04) : 1.00(±0.11) : 0.11(±0.04) [0.35(±0.07) : 1.00(±0.16):0.04+0.09-0.04]. We also present calculations of the capture rate coefficients for the two reactions, in which the interaction between the charge of the helium ion and the octupole moment of the methane molecule is included. The rotational-state-specific capture rate coefficients are calculated for states with J = (0-3) at collision energies below k B ·15 K. After averaging over the rotational states of methane populated at the rotational temperature of the supersonic beam, the calculations only predict extremely weak enhancements (in the order of ∼0.4%) of the rate coefficients compared to the Langevin rate constant k L over the collision-energy range considered.

We review the results of our recent experimental and theoretical studies of gas-phase ion-molecule reactions involving the He+ ion at low collision energies (Ecoll), in the kB⋅(0 - 40) K range. To avoid heating of the ions by stray electric fields, the reactions are studied within the orbit of a Rydberg electron. We reach collision energies down to ~0 K by employing a merged-beam setup. In the case of a molecule with a dipole moment (e.g., ammonia), we observe a strong enhancement of the measured reaction yield with decreasing Ecoll. This enhancement is attributed to rotational states which experience linear negative Stark shifts in the electric field of the ion. When the molecule has no dipole moment but a negative quadrupole moment (e.g., N2), we observe a suppression of the total reaction yield at the lowest collision energy. Our results are interpreted with the aid of an adiabatic-channel model., (Copyright 2022 Valentina Zhelyazkova. License: This work is licensed under a Creative Commons Attribution 4.0 International License.)

We report on an experimental and theoretical investigation of the He + + N 2 reaction at collision energies in the range between 0 and k B ·10 K. The reaction is studied within the orbit of a highly excited Rydberg electron after merging a beam of He Rydberg atoms (He( n ), n is the principal quantum number), with a supersonic beam of ground-state N 2 molecules using a surface-electrode Rydberg-Stark decelerator and deflector. The collision energy E coll is varied by changing the velocity of the He( n ) atoms for a fixed velocity of the N 2 beam and the relative yields of the ionic reaction products N + and N 2 + are monitored in a time-of-flight mass spectrometer. We observe a reduction of the total reaction-product yield of ∼30% as E coll is reduced from ≈ k B ·10 K to zero. An adiabatic capture model is used to calculate the rotational-state-dependent interaction potentials experienced by the N 2 molecules in the electric field of the He + ion and the corresponding collision-energy-dependent capture rate coefficients. The total collision-energy-dependent capture rate coefficient is then determined by summing over the contributions of the N 2 rotational states populated at the 7.0 K rotational temperature of the supersonic beam. The measured and calculated rate coefficients are in good agreement, which enables us to attribute the observed reduction of the reaction rate at low collision energies to the negative quadrupole moment, Q zz , of the N 2 molecules. The effect of the sign of the quadrupole moment is illustrated by calculations of the rotational-state-dependent capture rate coefficients for ion-molecule reactions involving N 2 (negative Q zz value) and H 2 (positive Q zz value) for | J , M 〉 rotational states with J ≤ 5 ( M is the quantum number associated with the projection of the rotational angular momentum vector J⃑ on the collision axis). With decreasing value of | M |, J⃑ gradually aligns perpendicularly to the collision axis, leading to increasingly repulsive (attractive) interaction potentials for diatomic molecules with positive (negative) Q zz values and to reaction rate coefficients that decrease (increase) with decreasing collision energies.