Cassini CAPS-ELS Observations of Negative Ions in Titan's Ionosphere: Solar Zenith Angle - Density Trends

2021 ◽  
Author(s):  
Anne Wellbrock ◽  
Andrew Coates ◽  
Geraint Jones ◽  
Richard Haythornthwaite ◽  
Oleg Shebanits ◽  
...  
Keyword(s):  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Electron Attachment ◽  
Negative Ions ◽  
Negative Ion ◽  
Unexpected Result ◽  
Cassini Mission ◽  
Haze Formation

<p>The discovery of heavy organic anions by in situ measurements using Cassini’s CAPS Electron Spectrometer (ELS) in Titan’s ionosphere was an unexpected result of the Cassini mission (Coates et al, 2007, Waite et al, 2007); a complete reconsideration of chemical processes in this enigmatic atmosphere was necessary as a result. These negative ions can be associated with complex hydrocarbon and nitrile processes which are linked to haze formation at lower altitudes. Cassini’s CAPS ELS observed negative ions during Titan encounters at altitudes below 1400 km. The ions can reach masses over 13,000 amu/q (Coates et al., 2009), while recurring peaks in the mass spectra can be used to identify different mass groups as reported by Coates et al. (2007) and Wellbrock et al. (2013, 2019). Studying density and mass trends of these groups helps to identify controlling factors of the production and destruction mechanisms, and ultimately to improve our understanding of how organic macromolecules can be produced by naturally occurring abiotic processes. In this study we examine the effects different solar zenith angle conditions might have on both the light and heavy negative ion mass groups, and consider the role of processes such as photodetachment and dissociative electron attachment. We also compare the negative ion data with RPWS electron measurements and discuss the possible implications associated with the above processes.</p>

scholarly journals Heavy negative ion growth in Titan’s polar winter

2019 ◽  
Vol 490 (2) ◽  
pp. 2254-2261
Author(s):  
A Wellbrock ◽  
A J Coates ◽  
G H Jones ◽  
V Vuitton ◽  
P Lavvas ◽  
...  
Keyword(s):  
Negative Ions ◽  
Large Data ◽  
Solar Flux ◽  
Negative Ion ◽  
Seasonal Effects ◽  
Unexpected Result ◽  
Data Set ◽  
Cassini Mission ◽  
First Time

ABSTRACT A significant but unexpected result of the Cassini mission was the discovery of heavy organic negative ions in Titan’s ionosphere at altitudes between about 950 and 1400 km by the CAPS Electron Spectrometer (ELS). The heaviest ions were observed during the T16 fly-by with masses over 13 000 u/q. This is significantly higher than the maximum masses observed during other fly-bys. We study T16 CAPS-ELS observations and examine the evolution of mass spectra at different altitudes. We also study maximum mass trends using a large data set from all available CAPS-ELS observations of the Cassini mission in order to investigate the conditions necessary to allow negative ions to grow to the highest masses. For the first time, we are able to investigate the relationship between the highest mass particles and seasonal effects. We find that the combination of high latitude and winter conditions, resulting in long-term restricted solar flux, create an environment in which ion growth can reach the highest masses, as observed during T16. Restricting solar flux long term, and hence photodestruction reactions such as photodetachment, appears to be essential for negative ions to grow beyond 10 000 u/q.

scholarly journals Role of Negative Ion Resonances in Electron Scattering from Atoms and Molecules

1999 ◽  
Vol 52 (3) ◽  
pp. 473 ◽  
Author(s):  
S. J. Buckman ◽  
D. T. Alle ◽  
M. J. Brennan ◽  
P. D. Burrow ◽  
J. C. Gibson ◽  
...  
Keyword(s):  
Electron Scattering ◽  
Cross Sections ◽  
Negative Ions ◽  
Negative Ion ◽  
Electron Correlations ◽  
Molecular Systems ◽  
Atoms And Molecules ◽  
Wide Range ◽  
Scattering Cross Sections

Transient negative ions (resonances) formed during the collision of an electron with an atom or molecule have been extensively studied for over thirty years. The continued interest in these states, both experimentally and theoretically, stems from the profound effects that they can have on electron scattering cross sections and the role that electron–electron correlations play in their formation and quasi-stability. A selective discussion of examples of such resonances, involving one, two and three excited electrons is given for a wide range of atomic and molecular systems.

scholarly journals A Laboratory Experiment for the Statistical Evaluation of Aerosol Retrieval (STEAR) Algorithms

2019 ◽  
Vol 11 (5) ◽  
pp. 498 ◽  
Author(s):  
Gregory Schuster ◽  
W. Espinosa ◽  
Luke Ziemba ◽  
Andreas Beyersdorf ◽  
Adriana Rocha-Lima ◽  
...  
Keyword(s):  
Particle Size ◽  
Laboratory Experiment ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Size Distributions ◽  
Shape Factors ◽  
Highly Correlated ◽  
Single Scatter ◽  
Absorption Measurements

We have developed a method for evaluating the fidelity of the Aerosol Robotic Network (AERONET) retrieval algorithms by mimicking atmospheric extinction and radiance measurements in a laboratory experiment. This enables radiometric retrievals that use the same sampling volumes, relative humidities, and particle size ranges as observed by other in situ instrumentation in the experiment. We use three Cavity Attenuated Phase Shift (CAPS) monitors for extinction and University of Maryland Baltimore County’s (UMBC) three-wavelength Polarized Imaging Nephelometer (PI-Neph) for angular scattering measurements. We subsample the PI-Neph radiance measurements to angles that correspond to AERONET almucantar scans, with simulated solar zenith angles ranging from 50 ∘ to 77 ∘ . These measurements are then used as input to the Generalized Retrieval of Aerosol and Surface Properties (GRASP) algorithm, which retrieves size distributions, complex refractive indices, single-scatter albedos, and bistatic LiDAR ratios for the in situ samples. We obtained retrievals with residuals less than 8% for about 90 samples. Samples were alternately dried or humidified, and size distributions were limited to diameters of less than 1.0 or 2.5 μ m by using a cyclone. The single-scatter albedo at 532 nm for these samples ranged from 0.59 to 1.00 when computed with CAPS extinction and Particle Soot Absorption Photometer (PSAP) absorption measurements. The GRASP retrieval provided single-scatter albedos that are highly correlated with the in situ single-scatter albedos, and the correlation coefficients ranged from 0.916 to 0.976, depending upon the simulated solar zenith angle. The GRASP single-scatter albedos exhibited an average absolute bias of +0.023–0.026 with respect to the extinction and absorption measurements for the entire dataset. We also compared the GRASP size distributions to aerodynamic particle size measurements, using densities and aerodynamic shape factors that produce extinctions consistent with our CAPS measurements. The GRASP effective radii are highly correlated (R = 0.80) and biased under the corrected aerodynamic effective radii by 1.3% (for a simulated solar zenith angle of θ ∘ = 50 ∘ ); the effective variance indicated a correlation of R = 0.51 and a relative bias of 280%. Finally, our apparatus was not capable of measuring backscatter LiDAR ratios, so we measured bistatic LiDAR ratios at a scattering angle of 173 degrees. The GRASP bistatic LiDAR ratios had correlations of 0.71 to 0.86 (depending upon simulated θ ∘ ) with respect to in situ measurements, positive relative biases of 2–10%, and average absolute biases of 1.8–7.9 sr.

Studies in Negative-Ion Mass Spectrometry. XII. Electron Attachment to a Series of Bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)-metal Complexes

1979 ◽  
Vol 32 (11) ◽  
pp. 2405 ◽  
Author(s):  
DR Dakternieks ◽  
IW Fraser ◽  
JL Garnett ◽  
IK Gregor
Keyword(s):  
Mass Spectra ◽  
Electron Attachment ◽  
Negative Ions ◽  
Fragmentation Pathway ◽  
Negative Ion ◽  
Metal Fluoride ◽  
Class A ◽  
Negative Ion Mass Spectrometry ◽  
Fragment Ions ◽  
Rearrangement Processes

Results of electron-attachment reactions in the gas phase as well as negative-ion mass spectra are given for a series of bis(1,1,1,5,5,5-hexafluoropentane-2,4-dionato)metal(1) complexes, (ML2), with the divalent metals MgII, MnII, Co11, Nil1, Cu11 and ZnII. While molecular, [ML2]- or [ML2]-, and ligand, [L]-, ions are present in the negative-ion mass spectra, the lability of the ligand C-F and C-CF3 bonds enables rearrangement processes involving fluorine atom transfers to become significant in the decompositions of both molecular and fragment ions, particularly for the class (a) metals, for which significant yields of [MLF2] and [MLF] negative ions were obtained. Thus, the predominant fragmentation pathway for such metal-containing complexes, for which metastable peaks have been assigned, occurs in the sequence [ML2]- -(*) → (MLF2]- - (8) → [L]- or alternatively [ML2]- -(*) → (MLF2]- - (8) → [L]- with the latter fragmentation in these sequences involving the elimination of the divalent metal fluoride, MF2.

scholarly journals Electron-induced chemistry in microhydrated sulfuric acid clusters

2017 ◽  
Author(s):  
Jozef Lengyel ◽  
Andriy Pysanenko ◽  
Michal Fárník
Keyword(s):  
Sulfuric Acid ◽  
Atmospheric Chemistry ◽  
Electron Attachment ◽  
Negative Ions ◽  
Ion Pair ◽  
Acid Water ◽  
Negative Ion ◽  
Water Molecules ◽  
Electron Recombination ◽  
Beam Experiment

Abstract. We investigate the mixed sulfuric acid-water clusters in a molecular beam experiment with electron attachment and negative ion mass spectrometry, and complement the experiment by DFT calculations. The microhydration of (H2SO4)m(H2O)n clusters is controlled by the expansion conditions, and the electron attachment yields the main cluster ion series (H2SO4)m(H2O)nHSO4− and (H2O)nH2SO4−. The mass spectra provide an experimental evidence for the onset of the ionic dissociation of sulfuric acid and ion-pair (HSO4− ··· H3O+) formation in the neutral H2SO4(H2O)n clusters with n ≥ 5 water molecules, in excellent agreement with the theoretical predictions. In the clusters with two sulfuric acid molecules (H2SO4)2(H2O)n this process starts already with n ≥ 2 water molecules. The (H2SO4)m(H2O)nHSO4− clusters are formed after the dissociative electron attachment to the clusters containing the (HSO4−···H3O+) ion-pair structure, which leads to the electron recombination with the H3O+ moiety generating H2O molecule and the H atom dissociation from the cluster. The (H2O)nH2SO4− cluster ions point to an efficient caging of the H-atom by the surrounding water molecules. The electron energy dependencies exhibit an efficient electron attachment at low electron energies below 3 eV, and no resonances above this energy, for all the measured mass peaks. This shows that in the atmospheric chemistry only the low-energy electrons can be efficiently captured by the sulfuric acid-water aerosols and converted into the negative ions. Possible atmospheric consequences of the acidic dissociation in the clusters and the electron attachment to the sulfuric acid-water aerosols are discussed.

Negative ions

1979 ◽  
Vol 293 (1400) ◽  
pp. 125-133 ◽  
Keyword(s):  
Mass Spectra ◽  
Chemical Ionization ◽  
Electron Attachment ◽  
Negative Ions ◽  
Negative Ion ◽  
Ionization Mass ◽  
Selected Ion Monitoring ◽  
Low Energy Electrons ◽  
High Concentrations ◽  
Positive Chemical Ionization

During the last few years, improvements in ionization techniques have revived interest in negative ion mass spectrometry and its applications. Ion sources that operate at pressures of up to 1 Torr (133 Pa) produce high concentrations of low energy electrons which may react directly with suitable sample molecules to form negative molecular and fragment ions. Alternatively, a reagent gas may be used to generate negative chemical ionization mass spectra which, in general, exhibit less fragmentation than many positive chemical ionization mass spectra. The sensitivity of the electron attachment processes may be very high for compounds containing electronegative elements and it may be enhanced for other compounds by making use of huorinated derivatives. Under chemical ionization conditions, reagent ions which react as Bransted bases frequently give [M —H] - ions in great abundance. Use of selected ion monitoring leads to sub-picogram detection levels in favourable cases. The gas phase ion chemistries of such ions as O -. and O 2 -. exhibit several unusual types of reaction which reveal further structural and mechanistic information, examples of which are discussed.

scholarly journals On the effective solar zenith and azimuth angles to use with measurements of hourly irradiation

2016 ◽  
Vol 13 ◽  
pp. 1-6 ◽  
Author(s):  
P. Blanc ◽  
L. Wald
Keyword(s):  
Time Series ◽  
Zenith Angle ◽  
Solar Zenith Angle ◽  
Azimuth Angle ◽  
High Quality ◽  
Direct Irradiation ◽  
Common Practices ◽  
Effective Angle ◽  
Yield Time

Abstract. Several common practices are tested for assessing the effective solar zenith angle that can be associated to each measurement in time-series of in situ or satellite-derived measurements of hourly irradiation on horizontal surface. High quality 1 min measurements of direct irradiation collected by the BSRN stations in Carpentras in France and Payerne in Switzerland, are aggregated to yield time series of hourly direct irradiation on both horizontal and normal planes. Time series of hourly direct horizontal irradiation are reconstructed from those of hourly direct normal irradiation and estimates of the effective solar zenith angle by one of the six practices. Differences between estimated and actual time series of the direct horizontal irradiation indicate the performances of six practices. Several of them yield satisfactory estimates of the effective solar angles. The most accurate results are obtained if the effective angle is computed by two time series of the direct horizontal and normal irradiations that should be observed if the sky were cloud-free. If not possible, then the most accurate results are obtained from using irradiation at the top of atmosphere. Performances show a tendency to decrease during sunrise and sunset hours. The effective solar azimuth angle is computed from the effective solar zenith angle.

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