1,721,044 research outputs found
Using NICE-OHVMS lineshapes to study relaxation rates and transition dipole moments
Full text linkNoise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS) is a successful technique that we have developed to sensitively, precisely, and accurately record transitions of molecular ions.\footnote{K.N. Crabtree \textit{et al.}, Chem. Phys. Lett. \textbf{551}, 1 (2012).} It has been used exclusively as a method for precise transition frequency measurement via saturation and fitting of the resultant Lamb dips. NICE-OHVMS has been employed to improve the uncertainties on \chem{H_3^+}, \chem{CH_5^+}, \chem{HeH^+}, and \chem{OH^+}, reducing the transition frequency uncertainties by two orders of magnitude.\footnote{J.N. Hodges \textit{et al.}, J. Chem. Phys. \textbf{139}, 164201 (2013).}\footnote{A.J. Perry \textit{et al.}, J. Mol. Spectrosc. \textbf{317}, 71 (2015).}\footnote{A.J. Perry \textit{et al.}, J. Chem. Phys. \textbf{141}, 101101 (2014).}\footnote{C.R. Marcus \textit{et al.}, Astrophys. J. \textbf{817}, 138 (2016).}
Because NICE-OHVMS is a saturation technique, this provides a unique opportunity to access information about the ratio of the transition dipole moment to the relaxation rate of the transition. This can be done in two ways, either through comparison of Lamb dip depth to the transition profile or comparison of the absorption intensity and dispersion intensity. Due to the complexity of the modulation scheme, there are many parameters that affect the apparent intensity of the recorded lineshape. A complete understanding of the lineshape is required to make the measurements of interest.
Here we present a model that accounts for the heterodyne modulation and velocity modulation, assuming that the fundamental lineshape is represented by a Voigt profile. Fits to data are made and interpreted in order to extract the saturation parameter.Made available in DSpace on 2017-01-26T21:40:10Z (GMT). No. of bitstreams: 3
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Previous issue date: 2016-06-2
In pursuit of a chemical and phenomenological understanding of long-living atmospheric pressure water-based ball plasmoids
Full text linkAtmospheric pressure water-based plasmoids have been studied for over a decade now,
however a large amount of information regarding how the plasmoid is impacted by the
parameters of the plasmoid generator and environment, and what chemical species are present in
the plasmoid has not been reported. To fill this gap, the geometry and the materials of the
plasmoid generator were varied greatly in order to determine how the plasmoid changes in
response to each of these parameters. Furthermore, the effect the atmosphere’s and
environment’s parameters have on the rising plasmoid was studied in a controlled environment.
Mass spectrometry of these plasmoids was also performed using an ion trap and an orbitrap in
order to identify the ions present in the plasmoid. These spectra revealed the presence of
(H2O)nH+ (n=2, 3), (H2O)nNO+ (n=0, 1), and several small molecules including H2O, NH3, and
NO3 bound to metal ions. Using isotopic labeling, these ions provided quantitative evidence
showing the plasmoid’s unique ability to protect its contents from mixing with the ambient air.Item withdrawn by Laura Spradlin ([email protected]) on 2014-03-17T13:13:48Z
Item was in collections:
University of Illinois Theses & Dissertations (ID: 1)
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Highly-accurate experimentally determined energy levels of H3+
Full text linkMade available in DSpace on 2019-07-15T22:16:36Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-06-19Made available in DSpace on 2020-01-25T19:31:08Z (GMT). No. of bitstreams: 4
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Previous issue date: 2019-06-19H is the simplest polyatomic molecule, and its rovibrational energy levels
provide valuable benchmarks for \textit{ab initio} theorists. Calculations of
the H potential energy surface which take into account effects beyond the
Born-Oppenheimer approximation can predict rovibrational transitions from low
lying states with an
accuracy of 0.001~cm,\footnote{L. G. Diniz, J. R.
Mohallem, A. Alijah, M. Pavanello, L. Adamowicz, O. L. Polyansky, and J.
Tennyson, \textit{Phys. Rev. A}, \textbf{88}, 032406 (2013).} and agreement is
on the order of 0.01--0.1~cm for transitions from higher levels. As the accuracy of theoretical methods begins to rival
experimental uncertainties, new measurements are needed to benchmark
future \textit{ab initio} calculations.
In order to provide accurate experimentally determined energy levels, a survey
of rovibrational transitions of H has been collected using the
sub-Doppler technique Noise-Immune Cavity-Enhanced Optical Heterodyne Velocity
Modulation Spectroscopy (NICE-OHVMS).\footnote{B. M. Siller, M. W. Porambo,
A. A. Mills, and B. J. McCall, \textit{Opt. Express}, \textbf{19},24822--7
(2011).} In total, we have measured 56
transitions in the fundamental band,\footnote{J. N. Hodges,
A. J. Perry, P. A. Jenkins II, B. M. Siller, and B. J. McCall, \textit{J. Phys.
Chem.}, \textbf{139}, 164201, (2013).}\footnote{A. J. Perry, J. N. Hodges, C. R.
Markus, G. S. Kocheril, and B. J. McCall, \textit{J. Mol. Spectrosc.},
\textbf{317},71--73, (2015).} 17 transitions in the
hot band, and 7 transitions in the
overtone band with approximately 4~MHz uncertainty. For
most transitions, this was an improvement by a factor of 40 or more.
Combination differences were used to calculate ground state rotational levels
relative to the lowest \textit{ortho} and \textit{para} states. A fit of the
ground vibrational state to an effective Hamiltonian was used to determine energy levels
relative to the forbidden (0,0) rotational state. Overall, 18 absolute energy levels were
determined with uncertainties of approximately 0.0003~cm (10~MHz). In
addition, frequencies of forbidden rotational transitions were predicted,
including a possible astrophysical maser.\footnote{J. H. Black, \textit{Faraday
Discussions}, \textbf{109}, 257--266 (1998).
Quantitative determination of lineshape parameters from velocity modulation spectroscopy
Full text linkVelocity Modulation Spectroscopy (VMS) has stood as the gold standard in molecular ion spectroscopy for 30 years. Whether in a traditional uni-directional experiment or more complicated cavity-enhanced layouts with additional layers of modulation, VMS remains the preferred ion detection scheme and is responsible for the detection and transition frequency determination of around 50 molecules.
Despite its success, VMS still has a great deal of untapped potential. There have only been two other published studies\footnote{H. Gao \textit{et al.}, Acta Phys. Sin. \textbf{50}, 1463 (2001).}\footnote{S. Civi\v{s}, Chem. Phys. \textbf{186}, 63 (1994).} of VMS lineshapes and both struggle with the highly correlated parameters: linewidth, intensity, and velocity modulation amplitude, \textit{i.e.} the maximum Doppler shift during a period of the discharge. Due to this difficulty, both Gao and Civi\v{s} made concessions to achieve a good fit. Careful analysis of the contour of the transition profile allows us to properly disentangle those parameters in order to probe the environment of the positive column. We can extract the precise values for the translational temperature of the ion, the relative transition intensity, the ion mobility, and the electric field strength just from the lineshape of a single transition. A firm understanding of the lineshape will facilitate chemical and physical investigations of positive columns and allow for a better understanding of more complicated detection schemes.Made available in DSpace on 2017-01-26T21:40:01Z (GMT). No. of bitstreams: 3
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Previous issue date: 2016-06-2
Development of a frequency-stabalized mid-infrared external Cavity-QCL cavity ringdown spectrometer
Full text linkExternal cavity quantum cascade lasers (EC-QCLs) provide significantly enhanced wavelength tunability while maintaining the high output powers of traditional QCLs throughout the mid-infrared portion of the spectrum. However, the inclusion of wavelength-selective moving parts allows vibrational and acoustic noise to be coupled into the laser as frequency and power noise. This can be particularly troublesome for cavity-enhanced spectroscopy, as attempts to increase vibrational isolation may interfere with stable cavity alignment.
Here, we discuss our efforts to improve the frequency stability of our EC-QCL while maintaining tunability and consistent cavity alignment. A mid-infrared hollow silica waveguide is used to vibrationally isolate the laser from the cavity while maintaining alignment. To further increase frequency stability, the laser is side-of-fringe locked to an uncoated solid germanium etalon. Tunability is maintained by incrementing the angle of incidence upon the etalon using a piezo-driven mirror. Angle of incidence tuning and automated periodic re-locking are managed using a BeagleBone Black development board. This allows us to maintain essentially continuous frequency tuning between 1140-1220 \wn while stabilizing the laser's frequency to within 30 MHz. Other mid-infrared frequencies could easily be accessed by swapping QCL chips.Made available in DSpace on 2014-09-17T16:56:18Z (GMT). No. of bitstreams: 3
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Previous issue date: 2014-06-1
Rotational equilibrium of C2 in interstellar clouds
No full textIn this work the understanding of the rotational equilibrium of C2 in interstellar clouds is updated. It is critical for this equilibrium to be well understood if C2 is to be used as a probe of the physical conditions in these clouds. Although new data continues to be published, the model was last updated in 1987. In this work, new data is collected and incorporated into the model using the program Radex, which will provide a standard format for sharing data, facilitate future updates, and enable the model to quickly run for a grid of temperature and density conditions.Item withdrawn by Mark Zulauf ([email protected]) on 2009-12-10T20:34:35Z
Item was in collections:
University of Illinois Theses & Dissertations (ID: 1)
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The nuclear spin dependence of the reaction of H3+ with H2 and the proposed spectroscopic investigation of HO2+
No full textHigh-resolution spectroscopy of molecular ions has been proven to be a difficult endeavor. Generating significant quantities of the desired ions and discriminating ions from neutrals are among some of the many difficulties surrounding the spectroscopic studies of these species. Despite these difficulties, molecular ions and their reactions play important roles as intermediates in organic reactions, reactants in combustion chemistry, species in biological processes such as respiration, as interstellar species, and as species found in terrestrial and extraterrestrial atmospheres. Although extensive research has been devoted to study these species and their reactions, scientists have barely ``scratched the surface'' in the realm of molecular ions.
One of the simplest molecular ions, H, has been measured spectroscopically in the laboratory and observed by astronomers in the interstellar medium, the galactic center, and planetary atmospheres. Both H and its parent neutral, H, exist in two nuclear spin configurations, \emph{ortho} and \emph{para}, and yield unique spectral signatures that can be measured in the laboratory and in astronomical environments. Most importantly, these species have been found to be useful temperature probes of interstellar clouds. However, a temperature discrepancy arises when comparing the temperatures calculated from each species. Since the chemistry of H has been well established, these findings indicate that the regulation of the nuclear spin states of H is not well understood.
The nuclear spin configuration of interstellar H is postulated to be governed by the reaction of H H H ~H and is one of the topics explored in this work. This reaction is investigated in the laboratory by spectroscopically monitoring the populations of several low-energy levels of \emph{ortho}- and \emph{para}-H in hydrogenic plasmas of varying \emph{para}-H enrichments. Measurements were taken at room temperature and for the first time, at liquid nitrogen temperatures. Steady-state modeling is employed to infer the ratio of the rates of the hop and exchange pathways of the above reaction and aids in the understanding of how the distribution of the nuclear spin states of H is regulated in the interstellar medium. This study will aid in understanding of the temperature discrepancy found between H and H in hopes to improve the viability of H as a temperature probe in astronomical environments where H measurements are impossible or not readily available.
Finally, a larger polyatomic molecular ion, HO, will be discussed in the final chapter. Although many simple polyatomic ions have been studied, the species HO has eluded detection for nearly three decades. Given the current theoretical information and past experimental attempts, a proposed experiment for the detection of this species is outlined.Item withdrawn by Mark Zulauf ([email protected]) on 2011-04-27T00:14:40Z
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CHARACTERIZATION AND INFRARED EMISSION SPECTROSCOPY OF BALL PLASMOID DISCHARGES
No full textPlasmas at atmospheric pressure serve many purposes, from ionization sources for ambient mass spectrometry (AMS) to plasma-assisted wound healing. Of the many naturally occurring ambient plasmas, ball lightning is one of the least understood; there is currently no solid explanation in the literature for the formation and lifetime of natural ball lightning. With the first measurements of naturally occurring ball lightning being reported last year,footnote{Cen, J.; Yuan, P,; Xue, S. textit{Phys. Rev. Lett.} textbf{2014}, textit{112}, 035001.} we have worked to replicate the natural phenomenon in order to elucidate the physical and chemical processes by which the plasma is sustained at ambient conditions.
We are able to generate ball-shaped plasmoids (self-sustaining plasmas) that are analogous to natural ball lightning using a high-voltage, high-current, pulsed DC system.footnote{Dubowsky, S.E.; Friday, D.M.; Peters, K.C.; Zhao, Z.; Perry, R.H.; McCall, B.J. textit{Int. J. Mass Spectrom.} textbf{2015}, textit{376}, 39-45.} Improvements to the discharge electronics used in our laboratory and characterization of the plasmoids that are generated from this system will be described. Infrared emission spectroscopy of these plasmoids reveals emission from water and hydroxyl radical -- fitting methods for these molecular species in the complex experimental spectra will be presented. Rotational temperatures for the stretching and bending modes of HO along with that of OH will be presented, and the non-equilibrium nature of the plasmoid will be discussed in this context
Nuclear Spin Dependence in Reactions of Hydrogen (3+) Ion in the Laboratory and the Interstellar Medium
No full textA comparison of the experimental results with observational data provides strong evidence that this reaction is the driving mechanism for the steady state enrichment of para- H+3 in diffuse clouds, and predictions from the models imply that it is also responsible for the enrichment of para- H+3 and para-H2 in dense clouds. The results of this work have implications for the use of the H+3 spin modifications as astrophysical probes, for understanding the deuterium chemistry of the interstellar medium, and for the fundamental chemical physics of these very simple molecules.Made available in DSpace on 2015-09-25T22:14:03Z (GMT). No. of bitstreams: 2
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Previous issue date: 2009Embargo set by: Seth Robbins for item 85629
Lift date: Forever
Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDsRestricted to the U of I community idenfinitely during batch ingest of legacy ETDsU of I Only159 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009
CHARACTERIZATION AND INFRARED EMISSION SPECTROSCOPY OF BALL PLASMOID DISCHARGES
Full text linkPlasmas at atmospheric pressure serve many purposes, from ionization sources for ambient mass spectrometry (AMS) to plasma-assisted wound healing. Of the many naturally occurring ambient plasmas, ball lightning is one of the least understood; there is currently no solid explanation in the literature for the formation and lifetime of natural ball lightning. With the first measurements of naturally occurring ball lightning being reported last year,footnote{Cen, J.; Yuan, P,; Xue, S. textit{Phys. Rev. Lett.} textbf{2014}, textit{112}, 035001.} we have worked to replicate the natural phenomenon in order to elucidate the physical and chemical processes by which the plasma is sustained at ambient conditions.
We are able to generate ball-shaped plasmoids (self-sustaining plasmas) that are analogous to natural ball lightning using a high-voltage, high-current, pulsed DC system.footnote{Dubowsky, S.E.; Friday, D.M.; Peters, K.C.; Zhao, Z.; Perry, R.H.; McCall, B.J. textit{Int. J. Mass Spectrom.} textbf{2015}, textit{376}, 39-45.} Improvements to the discharge electronics used in our laboratory and characterization of the plasmoids that are generated from this system will be described. Infrared emission spectroscopy of these plasmoids reveals emission from water and hydroxyl radical -- fitting methods for these molecular species in the complex experimental spectra will be presented. Rotational temperatures for the stretching and bending modes of HO along with that of OH will be presented, and the non-equilibrium nature of the plasmoid will be discussed in this context.Made available in DSpace on 2016-01-05T20:05:12Z (GMT). No. of bitstreams: 4
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Previous issue date: 2
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