Uptake of methanol on mixed HNO3/H2O clusters: An absolute pickup cross section.

The uptake of atmospheric oxidized organics on acid clusters is relevant for atmospheric new particle formation. We investigate the pickup of methanol (CH3OH) on mixed nitric acid-water clusters (HNO3)M(H2O)N by a combination of mass spectrometry and cluster velocity measurements in a molecular beam. The mass spectra of the mixed clusters exhibit (HNO3)m(H2O)nH+ series with m = 0-3 and n = 0-12. In addition, CH3OH·(HNO3)m(H2O)nH+ series with very similar patterns appear in the spectra after the methanol pickup. The velocity measurements prove that the undoped (HNO3)m(H2O)nH+ mass peaks in the pickup spectra originate from the neutral (HNO3)M(H2O)N clusters which have not picked up any CH3OH molecule, i.e., methanol has not evaporated upon the ionization. Thus the fraction of the doped clusters can be determined and the mean pickup cross section can be estimated, yielding σs¯≈ 20 Å2. This is compared to the lower estimate of the mean geometrical cross section σg¯≈ 60 Å2 obtained from the theoretical cluster geometries. Thus the "size" of the cluster corresponding to the methanol pickup is at least 3-times smaller than its geometrical size. We have introduced a method which can yield the absolute pickup cross sections relevant to the generation and growth of atmospheric aerosols, as illustrated in the example of methanol and nitric acid clusters.

Long time scale dynamics of vibrationally excited (HBr)n clusters.

We investigated the photodissociation dynamics of vibrationally excited HBr molecules and clusters. The species were generated in a molecular beam and excited with an IR laser to a v = 1 vibrational state. A subsequent ultraviolet (UV)-pulse with 243 nm radiation photolysed the molecules to yield H-fragments, which were resonantly ionized by the same UV-pulse (2 + 1 REMPI) and detected in a velocity map imaging (VMI) experiment. We performed action spectroscopy to distinguish between two expansion regimes: (i) expansion leading to isolated HBr molecules and (ii) generation of large (HBr)n clusters. Photodissociation of isolated HBr ( v = 1) molecules in particular J ro-vibrational states yielded faster H-fragments (by approximately 0.3 eV) with respect to the photodissociation of the ground state HBr ( v = 0). On the contrary, the IR excitation of molecules in (HBr) n clusters enhanced the yield of the H-fragments UV-photodissociated from the ground-state HBr ( v = 0) molecules. Our findings show that these molecules are photodissociated within clusters, and they are not free molecules evaporated from clusters after the IR excitation. Nanosecond IR-UV pump-probe experiments show that the IR-excitation enhances the H-fragment UV-photodissociation yield up to ∼100 ns after the IR excitation. After these long IR-UV delays, excitation of HBr molecules in clusters does not originate from the IR-excitation but from the UV-photodissociation and subsequent caging of HBr molecules in v > 0 states. We show that even after ∼100 ns the IR-excited larger (HBr) n clusters do not decay to individual molecules, and the excitation is still present in some form within these clusters enhancing their UV-photodissociation.

Imaging of rotational wave-function in photodissociation of rovibrationally excited HCl molecules.

We demonstrate a visualization of quantum mechanical phenomena with the velocity map imaging (VMI) technique, combining vibrationally mediated photodissociation (VMP) of a simple diatomic HCl with the VMI of its H-photofragments. Free HCl molecules were excited by a pump infrared (IR) laser pulse to particular rotational J levels of the v = 2 vibrational state, and subsequently a probe ultraviolet laser photodissociated the molecule at a fixed wavelength of 243.07 nm where also the H-fragments were ionized. The molecule was aligned by the IR excitation with respect to the IR laser polarization, and this alignment was reflected in the angular distribution of the H-photofragments. In particular, the highest degree of molecular alignment was achieved for the J=1←0 transition, which exclusively led to the population of a single rotational state with M = 0. The obtained images were analyzed for further details of the VMP dynamics, and different J states were studied as well. Additionally, we investigated the dynamic evolution of the excited states by changing the pump-probe laser pulse delay; the corresponding images reflected dephasing due to a coupling between the molecular angular momentum and nuclear spin. Our measurements confirmed previous observation using the time-of-flight technique by Sofikitis et al. [J. Chem. Phys. 127, 144307 (2007)]. We observed a partial recovery of the originally excited state after 60 ns in agreement with the previous observation.

Irregular shapes of water clusters generated in supersonic expansions.

We report cross sections for pickup of guest molecules on neutral argon and water clusters with the mean sizes in the range from N = 50 to 600. The experiments are supported by molecular dynamics simulations and analytical models based on the interaction potentials. The cross sections for argon clusters are consistent with their assumed spherical shape and follow approximately the theoretically justified N(1/3) dependence. On the other hand, the cross sections of water clusters depart from this dependence and are considerably larger starting from N ≥ 300. We interpret this increase of cross section by the occurrence of highly irregular shapes of water clusters produced in the supersonic expansion of water vapor under the conditions of the large cluster generation.

Imaging of hydrogen halides photochemistry on argon and ice nanoparticles.

The photodissociation dynamics of HX (X = Cl, Br) molecules deposited on large ArN and (H2O)N, N̄ ≈ 10(2)-10(3), clusters is investigated at 193 nm using velocity map imaging of H and Cl photofragments. In addition, time-of-flight mass spectrometry after electron ionization complemented by pickup cross section measurements provide information about the composition and structure of the clusters. The hydrogen halides coagulate efficiently to generate smaller (HX)n clusters on ArN upon multiple pickup conditions. This implies a high mobility of HX molecules on argon. On the other hand, the molecules remain isolated on (H2O)N. The photodissociation on ArN leads to strong H-fragment caging manifested by the fragment intensity peaking sharply at zero kinetic energy. Some of the Cl-fragments from HCl photodissociation on ArN are also caged, while some of the fragments escape the cluster directly without losing their kinetic energy. The images of H-fragments from HX on (H2O)N also exhibit a strong central intensity, however, with a different kinetic energy distribution which originates from different processes: the HX acidic dissociation followed by H3O neutral hydronium radical formation after the UV excitation, and the slow H-fragments stem from subsequent decay of the H3O. The corresponding Cl-cofragment from the photoexcitation of the HCl·(H2O)N is trapped in the ice nanoparticle.

Ionization of large homogeneous and heterogeneous clusters generated in acetylene-Ar expansions: cluster ion polymerization.

Pure acetylene and mixed Ar-acetylene clusters are formed in supersonic expansions of acetylene/argon mixtures and analysed using reflectron time-of-flight mass spectrometer with variable electron energy ionization source. Acetylene clusters composed of more than a hundred acetylene molecules are generated at the acetylene concentration of ≈8%, while mixed species are produced at low concentrations (≈0.7%). The electron energy dependence of the mass spectra revealed the ionization process mechanisms in clusters. The ionization above the threshold for acetylene molecule of 11.5 eV results in the main ionic fragment progression (C2H2)n(+). At the electron energies ≥21.5 eV above the CH+CH(+) dissociative ionization limit of acetylene the fragment ions nominally labelled as (C2H2)nCH(+), n ≥ 2, are observed. For n ≤ 7 these fragments correspond to covalently bound ionic structures as suggested by the observed strong dehydrogenation [(C2H2)n - k × H](+) and [(C2H2)nCH - k × H](+). The dehydrogenation is significantly reduced in the mixed clusters where evaporation of Ar instead of hydrogen can stabilize the nascent molecular ion. The C3H3(+) ion was previously assigned to originate from the benzene molecular ion; however, the low appearance energy of ≈13.7 eV indicates that a less rigid covalently bound structure of C6H6(+) ion must also be formed upon the acetylene cluster electron ionization. The appearance energy of Arn(C2H2)(+) fragments above ≈15.1 eV indicates that the argon ionization is the first step in the fragment ion production, and the appearance energy of Arn≥2(C2H2)m≥2(+) at ≈13.7 eV is discussed in terms of an exciton transfer mechanism.

Energy and charge transfer in ionized argon coated water clusters.

We investigate the electron ionization of clusters generated in mixed Ar-water expansions. The electron energy dependent ion yields reveal the neutral cluster composition and structure: water clusters fully covered with the Ar solvation shell are formed under certain expansion conditions. The argon atoms shield the embedded (H2O)n clusters resulting in the ionization threshold above ≈15 eV for all fragments. The argon atoms also mediate more complex reactions in the clusters: e.g., the charge transfer between Ar(+) and water occurs above the threshold; at higher electron energies above ~28 eV, an excitonic transfer process between Ar(+)* and water opens leading to new products Ar(n)H(+) and (H2O)(n)H(+). On the other hand, the excitonic transfer from the neutral Ar* state at lower energies is not observed although this resonant process was demonstrated previously in a photoionization experiment. Doubly charged fragments (H2O)(n)H2(2+) and (H2O)(n)(2+) ions are observed and Intermolecular Coulomb decay (ICD) processes are invoked to explain their thresholds. The Coulomb explosion of the doubly charged cluster formed within the ICD process is prevented by the stabilization effect of the argon solvent.

Uptake of atmospheric molecules by ice nanoparticles: pickup cross sections.

Uptake of several atmospheric molecules on free ice nanoparticles was investigated. Typical examples were chosen: water, methane, NO(x) species (NO, NO(2)), hydrogen halides (HCl, HBr), and volatile organic compounds (CH(3)OH, CH(3)CH(2)OH). The cross sections for pickup of these molecules on ice nanoparticles (H(2)O)(N) with the mean size of N≈260 (diameter ~2.3 nm) were measured in a molecular beam experiment. These cross sections were determined from the cluster beam velocity decrease due to the momentum transfer during the pickup process. For water molecules molecular dynamics simulations were performed to learn the details of the pickup process. The experimental results for water are in good agreement with the simulations. The pickup cross sections of ice particles of several nanometers in diameter can be more than 3 times larger than the geometrical cross sections of these particles. This can have significant consequences in modelling of atmospheric ice nanoparticles, e.g., their growth.

Cluster cross sections from pickup measurements: are the established methods consistent?

Pickup of several molecules, H(2)O, HBr, and CH(3)OH, and Ar atoms on free Ar(N) clusters has been investigated in a molecular beam experiment. The pickup cross sections of the clusters with known mean sizes, Ñ≈ 150 and 260 were measured by two independent methods: (i) the cluster beam velocity decrease due to the momentum transfer of the picked up molecules to the clusters, and (ii) Poisson distribution of a selected cluster fragment ion as a function of the pickup pressure. In addition, the pickup cross sections were calculated using molecular dynamics and Monte Carlo simulations. The simulations support the results of the velocity measurements. On the other hand, the Poisson distributions yield significantly smaller cross sections, inconsistent with the known Ar(N) cluster sizes. These results are discussed in terms of: (i) an incomplete coagulation of guest molecules on the argon clusters when two or more molecules are picked up; and (ii) the fragmentation pattern of the embedded molecules and their clusters upon ionization on the Ar cluster. We conclude that the Poisson distribution method has to be cautiously examined, if conclusions should be drawn about the cluster cross section, or the mean cluster size Ñ, and the number of picked up molecules.

Velocity map imaging of HBr photodissociation in large rare gas clusters.

We have implemented the velocity map imaging technique to study clustering in the pulsed supersonic expansions of hydrogen bromide in helium, argon, and xenon. The expansions are characterized by direct imaging of the beam velocity distributions. We have investigated the cluster generation by means of UV photodissociation and photoionization of HBr molecules. Two distinct features appear in the hydrogen atom photofragment images in the clustering regime: (i) photofragments with near zero kinetic energies and (ii) "hot" photofragments originating from vibrationally excited HBr molecules. The origin of both features is attributed to the fragment caging by the cluster. We discuss the nature of the formed clusters based on the change of the photofragment images with the expansion parameters and on the photoionization mass spectra and conclude that single HBr molecule encompassed with rare gas "snowball" is consistent with the experimental observations.

Vibrationally Mediated Stabilization of Electrons in Nonpolar Matter.

We explore solvation of electrons in nonpolar matter, here represented by butadiene clusters. Isolated butadiene supports only the existence of transient anions (resonances). Two-dimensional electron energy loss spectroscopy shows that the resonances lead to an efficient vibrational excitation of butadiene, which can result into the almost complete loss of energy of the interacting electron. Cluster-beam experiments show that molecular clusters of butadiene form stable anions, however only at sizes of more than 9 molecular units. We have calculated the distribution of electron affinities of clusters using classical and path integral molecular dynamics simulations. There is almost a continuous transition from the resonant to the bound anions with an increase in cluster size. The comparison of the classical and quantum dynamics reveals that the electron binding is strongly supported by molecular vibrations, brought about by nuclear zero-point motion and thermal agitation. We also inspected the structure of the solvated electron, finding it well localized.

Radiometry for the vertical electron cyclotron emission from the runaway electrons at the COMPASS tokamak.

Due to an increased interest in runaway electron (RE) phenomena in tokamak research, the need for diagnostics of runaway electron population in plasma has emerged. A novel diagnostic of the nonthermal electron cyclotron emission from runaway electrons can be utilized for this purpose. It was designed and installed at the COMPASS tokamak based on the available heterodyne radiometer. The vertical ECE (V-ECE) system uses a 16-channel heterodyne radiometer with a vertically placed E2-band horn antenna with a 76.5-90 GHz frequency range front-end. Simulations with the ray-tracing SPECE code have shown a measurement feasibility of the runaway electrons with energies up to 1 MeV. Due to a low optical depth of the plasma in COMPASS during RE discharges, reflected waves from the tokamak wall can be detected as well. First results show strong connection with other RE diagnostics at COMPASS. The V-ECE can obtain important information about RE population evolution and primary generation mechanism.

Influence of Polypharmacy on the Quality of Life in Stable Kidney Transplant Recipients.

BACKGROUND: Kidney transplant recipients are frequently treated for other medical conditions and experience polypharmacy. The aim of our study was to evaluate quality of life in relation to medicines' burden in these patients. METHODS: We studied 136 unselected patients with mean post-transplant time of 7.2 ± 4.6 years. Quality of life was evaluated using a validated Polish version of the Kidney Disease Quality of Life-Short Form questionnaire. Data concerning the type (generic name) and number of currently prescribed medications were collected by interview survey. The participants were divided into 3 groups: group 1, patients with a maximum of 4 different medications (n = 37); group 2, patients with 4 to 9 medications (n = 76); and group 3, patients receiving at least 10 different medications (n = 23). RESULTS: The number of medicines taken regularly ranged from 2 to 16. Patients with ≥10 drugs had the highest body mass index and lowest estimated glomerular filtration rate. Patients treated with ≥10 drugs, compared to patients from the 2 other groups, had presented lower subscales results concerning the physical functioning (65.9 vs 84.5 in group 1 and 83.4 in group 2, P < .001 for both comparisons), pain (57.2 vs 82.7 and 76.5, respectively, P < .001 for both), social function (66.8 vs 82.1 and 80.4, respectively, P = .04 for both), and energy/fatigue (54.8 vs 67.7, P = .03 and 65.4, P < .05). Multivariate regression analysis revealed that the number of drugs independently influenced physical functioning, pain, and social function subscales. CONCLUSIONS: Polypharmacy is associated with lower quality of life in patients after successful kidney transplantation. The negative impact of polypharmacy is particularly seen regarding physical functioning and pain severity.

Energy Transfer in Microhydrated Uracil, 5-Fluorouracil, and 5-Bromouracil.

Experiment and theory are combined to study the interaction of low energy electrons with microhydrated uracil and its halogenated analogues 5-fluorouracil and 5-bromouracil. We report electron ionization (EI) and electron attachment (EA) mass spectra for the uracils with different degrees of hydration. Both EI and EA lead to evaporation of water molecules. The number of evaporated molecules serves as a measure of the energy transferred to the solvent. Upon EI, the amount of energy transferred to neighboring water molecules is similar for all three studied species. On the other hand, the energy transferred upon EA rises significantly from uracil to 5-fluorouracil and 5-bromouracil. 5-Bromouracil is the only studied molecule that undergoes dissociative electron attachment after hydration at the studied energy of 1.2 eV. Theoretical modeling of the energetics for the electron attachment process allows for setting the energy transferred to the solvent on the absolute scale. We discuss the importance of this energy for the radiosensitization.

Microhydration Prevents Fragmentation of Uracil and Thymine by Low-Energy Electrons.

When ionizing radiation passes biological matter, a large number of secondary electrons with very low energies (<3 eV) is produced. It is known that such electrons cause an efficient fragmentation of isolated nucleobases via dissociative electron attachment. We present an experimental study of the electron attachment to microhydrated nucleobases. Our novel approach allows significant control over the hydration of molecules studied in the molecular beam. We directly show for the first time that the presence of a few water molecules suppresses the dissociative channel and leads exclusively to formation of intact molecular and hydrated anions. The suppression of fragmentation is ascribed to caging-like effects and fast energy transfer to the solvent. This is in contrast with theoretical prediction that microhydration strongly enhances the fragmentation of nucleobases. The current observation impacts mechanisms of reductive DNA strand breaks proposed to date on the basis of gas-phase experiments.

Past Cardiovascular Episodes Deteriorate Quality of Life of Patients With Type 1 Diabetes and End-stage Kidney Disease After Kidney or Simultaneous Pancreas and Kidney Transplantation.

BACKGROUND: The beneficial influence of kidney (KTx) or simultaneous pancreas and kidney transplantation (SPK) on quality of life (QOL) in patients with end-stage kidney disease caused by type 1 diabetes mellitus was confirmed in many studies. The aim of this study was to identify factors that influence QOL of patients in long-term follow-up after SPK or KTx. METHODS: Twenty-seven SPK and 26 KTx patients with good function of transplanted organs at least 1 year after transplantation were enrolled into the analysis. To estimate QOL of the recipients the Kidney Disease and Quality of Life Short Form was applied. RESULTS: Within the whole analyzed group, the necessity of exogenous insulin administration correlated (P < .05) with symptom/problem list (γ = -0.35), effects of kidney disease (-0.38), cognitive function (-0.47), sleep (-0.42), overall health (-0.47), physical functioning (-0.61), role-physical (-0.32), pain (-0.50), general health (-0.32), emotional well-being (-0.31), role-emotional (-0.36), social function (-0.33), energy/fatigue (-0.44), and the SF-12 physical composite (-0.44). History of cardiovascular episode correlated (P < .05) with symptom/problem list (γ = -0.59), effects of kidney disease (-0.46), burden of kidney disease (-0.56), sleep (-0.54), social support (-0.51), physical functioning (-0.55), role-physical (-0.70), pain (-0.60), general health (-0.57), emotional well-being (-0.45), role-emotional (-0.95), social function (-0.58), energy/fatigue (-0.59), SF-12 physical composite (-0.45), and SF-12 mental composite (-0.83). CONCLUSIONS: Exogenous insulin administration and history of cardiovascular episode are the most important factors influencing QOL in patients after SPK or KTx, particularly worsening its physical components.

Isomeric transitions in size-selected methanol hexamers probed by OH-stretch spectroscopy.

We have measured the isomeric transition between the energetically lowest lying isomers of S6 and C2-symmetry of (CH3OH)6. The clusters are size-selected by deflection in collisions with He, and the isomers are identified by their infrared spectra of the OH-stretching vibration. The measurements are carried out at three source temperatures 253, 300 and 373 K which correspond to the cluster temperatures 93, 106 and 135 K. The latter ones are estimated by a relaxation model that accounts for the cluster formation and the energy released by the condensation. The transition takes place at a cluster temperature of about 102 K which is in agreement with the Molecular Dynamics simulation of such a transition at about 117 K using a realistic model potential.

Comparative FTIR spectroscopy of HX adsorbed on solid water: Ragout-jet water clusters vs ice nanocrystal arrays.

In addition to revealing the stretch-mode bands of the smallest mixed clusters of HCl and HBr (HX) with water, the ragout-jet FTIR spectra of dense mixed water-acid supersonic jets include bands that result from the interaction of HX with larger water clusters. It is argued here that low jet temperatures prevent the water-cluster-bound HX molecules from becoming sufficiently solvated to induce ionic dissociation. The molecular nature of the HX can be deduced directly from the observed influence of changing from HCl to HBr and from replacing H2O with D2O. Furthermore, the band positions of HX are roughly coincidental with bands assigned to molecular HCl and HBr adsorbed on ice nanocrystal surfaces at temperatures below 100 K. It is also interesting that the HX band positions and widths approximate those of HX bound to the surface of amorphous ice films at <60 K. Though computational results suggest the adsorbed HX molecules observed in the jet expansions are weakly distorted by single coordination with surface dangling-oxygen atoms, on-the-fly trajectories indicate that the cluster skeletons undergo large-amplitude low-frequency vibrations. Local HX solvation, the extent of proton sharing, and the HX vibrational spectra undergo serious modulation on a picosecond time scale.

High-resolution IR studies of hydrogen bonded clusters: large amplitude dynamics in (HCl)n.

Structural and dynamical information on small hydrogen-bonded systems is revealed by high-resolution IR spectroscopy of HCl dimer, trimer and tetramer. In (HCl)2, four combination bands tentatively assigned to the Van der Waals stretch nu 4 and geared band nu 5 vibrations are observed. The study focuses on two unexpected results: (i) all of the observed bands are built only on the bound HCl stretch nu 2, and (ii) the bands predominantly originate from the 9-fold less populated upper tunneling level of the ground state. Model 3D quantum calculations are presented to show that both these surprising trends originate from the large amplitude tunneling dynamics in the dimer. The (HCl)3 spectra are assigned and analyzed for multiple isotopomeric contributions. The spectral fit reveals large homogeneous line broadening indicating the excited state lifetime of approximately 1.6 ns and tentatively associated with dynamics of intramolecular vibrational energy distribution (IVR) induced trimer ring opening. Finally, first high-resolution data on the HCl stretch fundamental spectrum of (HCl)4 are presented.