A new setup for measurements of absolute saturation vapor pressures using a dynamical method: Experimental concept and validation.

We describe a new experimental system for direct measurements of the absolute saturation vapor pressures of liquid or solid samples. The setup allows the isolation of the sample under steady conditions in an ultra-high vacuum chamber, where the measurement of the sample's vapor pressure as a function of its temperature can be performed in a range around room temperature and in a pressure range defined only by the applied absolute pressure sensor. We characterize the setup and illustrate its capability to measure saturation vapor pressures as well as enthalpies of evaporation around room temperature with explicit measurements on four liquid compounds (diethyl phthalate, 1-decanol, 1-heptanol, and 1-hexanol) for which accurate vapor pressures have previously been reported.

Gas-to-Particle Partitioning of Products from Ozonolysis of Δ3-Carene and the Effect of Temperature and Relative Humidity.

Formation of oxidized products from Δ3-carene (C10H16) ozonolysis and their gas-to-particle partitioning at three temperatures (0, 10, and 20 °C) under dry conditions (<2% RH) and also at 10 °C under humid (78% RH) conditions were studied using a time-of-flight chemical ionization mass spectrometer (ToF-CIMS) combined with a filter inlet for gases and aerosols (FIGAERO). The Δ3-carene ozonolysis products detected by the FIGAERO-ToF-CIMS were dominated by semivolatile organic compounds (SVOCs). The main effect of increasing temperature or RH on the product distribution was an increase in fragmentation of monomer compounds (from C10 to C7 compounds), potentially via alkoxy scission losing a C3 group. The equilibrium partitioning coefficient estimated according to equilibrium partitioning theory shows that the measured SVOC products distribute more into the SOA phase as the temperature decreases from 20 to 10 and 0 °C and for most products as the RH increases from <2 to 78%. The temperature dependency of the saturation vapor pressure (above an assumed liquid state), derived from the partitioning method, also allows for a direct way to obtain enthalpy of vaporization for the detected species without accessibility of authentic standards of the pure substances. This method can provide physical properties, beneficial for, e.g., atmospheric modeling, of complex multifunctional oxidation products.

Excited-state dynamics and fluorescence lifetime of cryogenically cooled green fluorescent protein chromophore anions.

Time-resolved action spectroscopy together with a fs-pump probe scheme is used in an electrostatic ion-storage ring to address lifetimes of specific vibrational levels in electronically excited states. Here we specifically consider the excited-state lifetime of cryogenically cooled green fluorescent protein (GFP) chromophore anions which is systematically measured across the S0-S1 spectral region (450-482 nm). A long lifetime of 5.2 ± 0.3 ns is measured at the S0-S1 band origin. When exciting higher vibrational levels in S1, the lifetime changes dramatically. It decreases by more than two orders of magnitude in a narrow energy region ∼250 cm-1 (31 meV) above the 0-0 transition. This is attributed to the opening of internal conversion over an excited-state energy barrier. The applied experimental technique provides a new way to uncover even small energy barriers, which are crucial for excited-state dynamics.

Secondary ionization of pyrimidine nucleobases and their microhydrated derivatives in helium nanodroplets.

Radiation damage in biological systems by ionizing radiation is predominantly caused by secondary processes such as charge and energy transfer leading to the breaking of bonds in DNA. Here, we study the fragmentation of cytosine (Cyt) and thymine (Thy) molecules, clusters and microhydrated derivatives induced by direct and indirect ionization initiated by extreme-ultraviolet (XUV) irradiation. Photofragmentation mass spectra and photoelectron spectra of free Cyt and Thy molecules are compared with mass and electron spectra of Cyt/Thy clusters and microhydrated Cyt/Thy molecules formed by aggregation in superfluid helium (He) nanodroplets. Penning ionization after resonant excitation of the He droplets is generally found to cause less fragmentation compared to direct photoionization and charge-transfer ionization after photoionization of the He droplets. When Cyt/Thy molecules and oligomers are complexed with water molecules, their fragmentation is efficiently suppressed. However, a similar suppression of fragmentation is observed when homogeneous Cyt/Thy clusters are formed in He nanodroplets, indicating a general trend. Penning ionization electron spectra (PIES) of Cyt/Thy are broad and nearly featureless but PIES of their microhydrated derivatives point at a sequential ionization process ending in unfragmented microsolvated Cyt/Thy cations.

Electron energy loss and angular asymmetry induced by elastic scattering in superfluid helium nanodroplets.

Helium nanodroplets are ideal model systems to unravel the complex interaction of condensed matter with ionizing radiation. Here we study the effect of purely elastic electron scattering on angular and energy distributions of photoelectrons emitted from He nanodroplets of variable size (10-109 atoms per droplets). For large droplets, photoelectrons develop a pronounced anisotropy along the incident light beam due to a shadowing effect within the droplets. In contrast, the detected photoelectron spectra are only weakly perturbed. This opens up possibilities for photoelectron spectroscopy of dopants embedded in droplets provided they are smaller than the penetration depth of the light and the trapping range of emitted electrons in liquid helium.

High-Resolution Spectroscopy and Selective Photoresponse of Cryogenically Cooled Green Fluorescent Protein Chromophore Anions.

By time-resolved action spectroscopy of cryogenically cooled molecular ions, we have achieved a remarkable vibrational resolution in the photoresponse of the deprotonated green fluorescent protein (GFP) chromophore, a key molecular unit in the bioimaging of living cells. We define four characteristic spectral regions of the S0-S1 band with competing electronic and nuclear decay channels. We determine the energy barrier toward internal conversion to be ∼250 cm-1. This inhibits internal conversion and hence statistical fragmentation near the S0-S1 band origin, which is identified at 481.51 ± 0.15 nm (20768 ± 6 cm-1). The origin is red-shifted by only 221 cm-1 compared to that of wild-type GFP at 77 K. This, together with a striking agreement between the vibronic profiles of the protein and its chromophore, suggests their similar photophysics. In combination with theory, the data reveal the coexistence of mutually energy-borrowing mechanisms between nuclei and electrons mediated by specific vibrational modes.

Dopant ionization and efficiency of ion and electron ejection from helium nanodroplets.

Photoionization spectroscopy and mass spectrometry of doped helium (He) nanodroplets rely on the ability to efficiently detect ions and/or electrons. Using a commercial quadrupole mass spectrometer and a photoelectron-photoion coincidence spectrometer, we systematically measure yields of ions and electrons created in pure and doped He nanodroplets in a wide size range and in two ionization regimes-direct ionization and secondary ionization after resonant photoexcitation of the droplets. For two different types of dopants (oxygen molecules, O2, and lithium atoms, Li), we infer the optimal droplet size to maximize the yield of ejected ions. When dopants are ionized by charge-transfer to photoionized He nanodroplets, the highest yield of O2 and Li ions is detected for a mean size of ∼5×104 He atoms per nanodroplet. When dopants are Penning ionized via photoexcitation of the He droplets, the highest yield of O2 and Li ions is detected for ∼103 and ∼105 He atoms per droplet, respectively. At optimum droplet sizes, the detection efficiency of dopant ions in proportion to the number of primary photoabsorption events is up to 20% for charge-transfer ionization of O2 and 2% for Li, whereas for Penning ionization it is 1% for O2 and 4% for Li. Our results are instrumental in determining optimal conditions for mass spectrometric studies and photoionization spectroscopy of molecules and complexes isolated in He nanodroplets.

An electron-ion coincidence spectrometer for commissioning of a synchrotron radiation beamline: Absolute photon intensity and content of higher harmonic radiation.

We describe the commissioning of a new electron-ion coincidence spectrometer used to diagnose the photon beam from a plane grating monochromator beamline at the ASTRID2 synchrotron radiation facility. The spectrometer allows determination of the absolute photon intensity by calibration to the photoabsorption cross sections of known gases, such as the rare gases Ar, Kr, and Xe presented here. The spectrometer operates at very low pressure (∼10-8-10-9 mbar) and-due to the coincidence electron-ion detection scheme-the detector efficiencies can be determined routinely; hence, the spectrometer can be recalibrated swiftly. By variation of a single potential of the spectrometer, the content of higher order radiation in the monochromatized synchrotron radiation can be analyzed. The layout and operation of the synchrotron radiation beamline at ASTRID2 and its additional photon diagnostic units are additionally described.

A new endstation for extreme-ultraviolet spectroscopy of free clusters and nanodroplets.

In this work, we present a new endstation for the AMOLine of the ASTRID2 synchrotron at Aarhus University, which combines a cluster and nanodroplet beam source with a velocity map imaging and time-of-flight spectrometer for coincidence imaging spectroscopy. Extreme-ultraviolet spectroscopy of free nanoparticles is a powerful tool for studying the photophysics and photochemistry of resonantly excited or ionized nanometer-sized condensed-phase systems. Here, we demonstrate this capability by performing photoelectron-photoion coincidence experiments with pure and doped superfluid helium nanodroplets. Different doping options and beam sources provide a versatile platform to generate various van der Waals clusters as well as He nanodroplets. We present a detailed characterization of the new setup and show examples of its use for measuring high-resolution yield spectra of charged particles, time-of-flight ion mass spectra, anion-cation coincidence spectra, multi-coincidence electron spectra, and angular distributions. A particular focus of the research with this new endstation is on intermolecular charge and energy-transfer processes in heterogeneous nanosystems induced by valence-shell excitation and ionization.

The reaction of isotope-substituted hydrated iodide I(HO)- with ozone: the reactive influence of the solvent water molecule.

We report an investigation of the reaction of isotope-substituted hydrated iodide I(HO)- with ozone 16O3 to examine the involvement of the water molecules in the oxidation reactions that terminate with the formation of IO3-. Experimentally, we studied the reaction in the gas phase as elementary reactions using a radio-frequency (RF) ion-trap combined with a quadrupole mass spectrometer (QMS). In approximately 1.2% of the reactions of I(HO)- and 16O3, the 18O atom is found to appear in iodine oxide anions, thus giving evidence for a close involvement of the water molecule in a non-negligible number of the reactions towards IO3-. As a part of the experimental investigation, the reaction rate constant for the exchange reaction I(HO)- + HO → I(HO)- + HO at 300 K was found to be (1.3 ± 0.1) × 10-8 cm3 s-1. Quantum chemical calculations are exploited to establish the energetic difference between I(HO)- and I(HO)-.

Reply to the 'Comment on "Atmospheric chemistry of iodine anions: elementary reactions of I-, IO-, and IO with ozone studied in the gas-phase at 300 K using an ion trap"' by D. Britz, Phys. Chem. Chem. Phys., 2019, 21, C9CP03851E.

We reply to the comment by Dieter Britz on two recent papers in Physical Chemistry Chemical Physics. The comment presents a valuable, however, less flexible, alternative to the analysis performed in these papers and as such has no impact on any of the scientific results reported in the two publications.

The reaction of hydrated iodide I(H2O)- with ozone: a new route to IO2- products.

We report on an experimental characterization of the isolated reaction of hydrated iodide I(H2O)- with ozone O3 at room temperature performed using a radio-frequency ion trap combined with a quadrupole mass spectrometer. Contrary to the oxidation reaction of the bare I- ion, the hydrated iodide I(H2O)- primarily reacts to form I- and IO2- with significant absolute reaction rate constants of 2.0 ± 0.3 × 10-10 cm3 molecule-1 s-1 and 2.5 ± 0.3 × 10-10 cm3 molecule-1 s-1 while direct pathways to IO- and IO3- are much weaker. Quantum chemical calculations indicate that in aqueous phase and for atmospherically relevant temperatures, the presence of hydrated iodides are favored over bare I- ions, thus suggesting that the chemistry of the hydrated ions is relevant for understanding and modeling atmospheric processes at the air-water interface.

Atmospheric chemistry of iodine anions: elementary reactions of I-, IO-, and IO2- with ozone studied in the gas-phase at 300 K using an ion trap.

Using a radio-frequency ion trap to study ion-molecule reactions under isolated conditions, we report a direct experimental determination of reaction rate constants for the sequential oxidation of iodine anions by ozone at room temperature (300 K). The results are R1: I- + O3 → IO- + O2, k1 = (7 ± 2) × 10-12 cm3 s-1; R2: IO- + O3 → IO2- + O2, k2 = (10 ± 2) × 10-9 cm3 s-1; R3: IO2- + O3 → IO3- + O2, k3 = (16 ± 2) × 10-9 cm3 s-1. More oxidized forms such as IO4- and IO5- were not observed. Additionally, we performed quantum chemical calculations to elucidate the energetics of these oxidation reactions.

Origin of the Intrinsic Fluorescence of the Green Fluorescent Protein.

Green fluorescent protein, GFP, has revolutionized biology, due to its use in bioimaging. It is widely accepted that the protein environment makes its chromophore fluoresce, whereas the fluorescence is completely lost when the native chromophore is taken out of GFP. By the use of a new femtosecond pump-probe scheme, based on time-resolved action spectroscopy, we demonstrate that the isolated deprotonated GFP chromophore can be trapped in the first excited state when cooled to 100 K. The trapping is shown to last for 1.2 ns, which is long enough to establish conditions for fluorescence and consistent with calculated trapping barriers in the electronically excited state. Thus, GFP fluorescence is traced back to an intrinsic chromophore property, and by improving excited-state trapping, protein interactions enhance the molecular fluorescence.

Decoupling Electronic versus Nuclear Photoresponse of Isolated Green Fluorescent Protein Chromophores Using Short Laser Pulses.

The photophysics of a deprotonated model chromophore for the green fluorescent protein is studied by femtosecond laser pulses in an electrostatic ion-storage ring. The laser-pulse duration is much shorter than the time for internal conversion, and, hence, contributions from sequential multiphoton absorption, typically encountered with ns-laser pulses, are avoided. Following single-photon excitation, the action-absorption maximum is shown to be shifted within the S_{0} to S_{1} band from its origin at about 490 to 450 nm, which is explained by the different photophysics involved in the detected action.

Analysis of ionic photofragments stored in an electrostatic storage ring.

A new method to analyze the properties of fragment ions created in storage ring experiments is presented. The technique relies on an acceleration of ionic fragments immediately after production whereby the fragments are stored in the storage ring. To obtain a fragment mass spectrum, the storage ring is exploited as an electrostatic analyzer (ESA) in which case the number of stored fragment ions is recorded as a function of the applied acceleration potential. However, the storage ring can additionally be employed as a time-of-flight (TOF) instrument by registering the temporal distribution of fragment ions. It is demonstrated that the combined ESA-TOF operation of the ring allows not only to determine fragment masses with much better resolution compared to the ESA mode alone but also enables the extraction of detailed information on the fragmentation dynamics. The method is described analytically and verified with photodissociation experiments on stored Cl2 (-) at an excitation wavelength of 530 nm.

Does age affect prognosis in salivary gland carcinoma patients? A national Danish study.

AIM: To compare incidence, histology, treatment modalities, disease stages, and outcome in elderly patients (≥70 years) compared to younger (<70 years). METHODS: From the national Danish salivary gland carcinoma database, 871 patients diagnosed with a primary salivary gland carcinoma from January 1990 to December 2005 were identified. Variables necessary for statistical analyses were extracted from the database. RESULTS: The younger patients have a significantly better crude, disease-specific and recurrence-free survival than the elderly ones. In univariate analysis, significantly more patients in the young group were WHO performance status 0 and in disease stage I + II, and they presented with significantly more histological low grade tumors. In multivariate analysis, chronological age seemed to be of no prognostic significance to salivary gland carcinoma patients as opposed to performance status, disease stage and histological grade. CONCLUSIONS: Salivary gland carcinoma patients over the age of 70 years have a poor prognosis compared to younger patients, which can be explained by higher disease stages, more histological high grade subtypes and a poorer performance status at the time of diagnosis.

Salivary adenoid cystic carcinoma in Denmark 1990-2005: Outcome and independent prognostic factors including the benefit of radiotherapy. Results of the Danish Head and Neck Cancer Group (DAHANCA).

AIM: To describe outcome and prognostic factors, including the effect of radiotherapy, in a consecutive national series of salivary gland adenoid cystic carcinomas. METHODS: From the national Danish salivary gland carcinoma database in the structure of DAHANCA, 201 patients diagnosed with adenoid cystic carcinoma, and treated with a curative intent, were identified in the period between 1990 and 2005. Variables necessary for statistical analyses were extracted from the database. RESULTS: The 10-year crude survival and disease specific survival rates were 58% and 75%, respectively. The 10-year locoregional control rate was 70%, and 36% of patients experienced a recurrence during follow-up (median 7.5 years); 18% developed distant metastases (most commonly to the lungs). In multivariate analysis, stage and margin status were both important factors with regards to survival and locoregional control. Radiotherapy did not improve survival, but it did improve the locoregional control rate. CONCLUSIONS: The treatment of choice is surgery with as wide margins as possible including elective, selective neck dissection. Adjuvant radiotherapy should be considered in patients with incomplete tumor resection, high disease stages, and tumors with a solid growth pattern.

Abnormal rhythmic oscillations of atrial natriuretic peptide and brain natriuretic peptide in chronic renal failure.

Secretion of ANP (atrial natriuretic peptide) and BNP (brain natriuretic peptide) is pulsatile in healthy humans. However, the patterns of secretion of ANP and BNP have not been studied in chronic renal failure. The aim of the present study was to test the hypotheses that ANP and BNP are secreted in pulses in dialysis patients, and that pulsatile secretion is regulated by prostaglandins. Blood samples were drawn every 2 min through an intravenously inserted plastic needle over a period of 1-2 h in 13 dialysis patients and 13 healthy control subjects (Study 1), and in 15 healthy control subjects, who participated in a randomized placebo-controlled cross-over study after treatment with indomethacin and placebo (Study 2). Plasma concentrations of ANP and BNP were determined by RIAs, and the results were analysed for pulsatile behaviour by Fourier transformation. The results from Study 1 showed that the secretion of ANP and BNP was pulsatile in nine patients with chronic renal failure. The maximum amplitude was significantly higher in chronic renal failure compared with control subjects for both ANP and BNP (ANP, 4.3 compared with 0.7 pmol/l; BNP, 2.0 compared with 0.3 pmol/l; values are medians) and correlated positively with the mean plasma level of ANP (rho=0.900, P=0.001; n=9) and BNP (rho=0.983, P=0.000; n=9). The frequency was the same for patients and controls. The results from Study 2 demonstrated pulsatile secretion in all subjects, but both the amplitude and frequency were unaffected by indomethacin. The maximum amplitude correlated positively with the mean plasma level of ANP and BNP during both placebo and indomethacin treatment. It can be concluded that the secretion of ANP and BNP is pulsatile with abnormally high amplitude in chronic renal failure, that prostaglandins apparently are not involved in the secretion of these peptides in healthy subjects and that the high secretion rate in chronic renal failure results in higher ANP and BNP in plasma.