McCall Research Group Illinois

High Resolution Mid-IR Spectroscopy With Quantum Cascade Lasers

Introduction

Fabry-Perot quantum cascade laser
The Fabry-Perot quantum cascade laser used to perform high-resolution spectroscopy near 8.5 microns.

In the McCall group we have constructed a Fabry-Perot quantum cascade laser (FP-QCL) based continuous-wave cavity ringdown spectrometer (cw-CRDS) coupled to a supersonic expansion source. Development of the instrument is the result of a collaboration with Professor Claire Gmachl's group at Princeton University. The primary purpose of the spectrometer is to enable high resolution rovibrational spectroscopy of a rotationally and vibrationally cold gas phase sample of Buckminsterfullerene (C60) around ~8.5 microns. In addition to the C60 spectroscopic search, we are continuing to develop our instrument for other high resolution gas phase mid-IR spectroscopy projects.

C60 Spectroscopic Interest

C60 is of fundamental spectroscopic interest because of its high degree of symmetry. C60 is a member of the Ih point group. Because of the high symmetry only 12 out of 174 vibrational modes ( the 4 triply degenerate F1u representations) are IR active. Additional symmetry consequences arise given an isotopically pure molecule composed entirely of spin-0 12C bosons. Only certain rotational levels in the ground state are allowed to exist based upon symmetry constraints laid out by the Pauli principle. Because of these symmetry considerations we expect missing transitions in the rovibrational band due to missing levels in the ground state with forbidden symmetry.

C60 Astronomical Interest

C60 was discovered in experiments of carbon-rich stellar outflows. Carbon-rich stars are therefore a likely source of C60 that could diffuse into interstellar space. After the laboratory discovery, C60 has been found in meteorite impact sediments and associated with impact craters on the Long Duration Exposure Facility. Though the C60 found in both of these sources cannot conclusively be identified as extraterrestrial in origin, they do provide indirect evidence for the possibility of C60 outside of the solar system. Recently, the first astronomical detection of C60 was made through infrared emission observations from the protoplanetary nebula Tc1. The detected C60 was found to be embedded in dust grains. A high-resolution gas-phase spectrum will provide an essential roadmap for identifying spectral features belonging to gas-phase C60 in an astronomical search. Detections of gas phase C60 in other environments will aid in understanding the interstellar chemistry of this unique molecular species.

Other Spectroscopic Targets

Pyrene (C16H10) Spectroscopy
Pyrene spectrum
Comparison of the experimental and simulated spectra of the ν68 vibrational band of pyrene.

High-resolution infrared spectroscopy is typically performed on small molecules because they are easy generate in the gas phase and have large rotational constants, making it easier to resolve individual rotational levels. We are interested in extending high-resolution spectroscopy to larger molecules, so we have used our spectrometer to measure the ν68 vibrational mode (in plane hydrogen wag) of pyrene, a polycyclic aromatic hydrocarbon. This is the largest molecule that has ever been observed with rotational resolution by infrared absorption spectroscopy. The entire band was observed by heating the pyrene to 160 Celsius in our high temperature oven and cooling the molecules in a supersonic slit expansion before recording the spectrum with our QCL cavity ringdown spectrometer.

Deuterated Water Clusters
Dimer spectrum
The Q-branch region of the Ka = 2 ← 1 sub-band of the bending mode of (D2O)2 as measured by our QCL spectrometer.

Our QCL spectrometer also has frequency coverage in the region of the bending mode of D2O. We have used our spectrometer to obtain high-resolution spectra of small deuterated water clusters, including Ar-D2O and (D2O)2. Small water clusters are important model systems for understanding the complex interactions that occur in liquid water, and high-resolution spectra give detailed information about the interactions between water molecules. Water dimer is an especially important system because it provides information about the two-body interactions between water molecules. We have obtained rotationally-resolved spectra of the bending modes of (D2O)2, which are the first high-resolution spectra of the bending mode of any water dimer.



Instrument Development

Supercritical Fluid Supersonic Expansion Source

While we have successfully been able to observe pyrene by simply heating it in an oven, this approach has not worked for C60 because it must be heated to a much higher temperature to be vaporized. Because the molecules start very hot (near 1000 K) they cannot be sufficiently cooled vibrationally by a supersonic expansion. To get around this problem we are working on a new way to generate gas phase C60 by dissolving it in a supercritical fluid at lower temperatures and then using a supersonic expansion to cool the molecules. With this technique, we should be able to generate gas phase C60 at a much lower temperature, which should be easier to cool vibrationally.

External Cavity QCL System

One problem with QCLs that has limited their wide adoption is the fact that a single QCL can only cover a small frequency region. Newer QCLs have been developed which can cover much broader frequency regions, allowing a single laser to be used for many different molecular targets. We are working in collaboration with Gerard Wysocki's group at Princeton to develop our own broadly tunable QCL system to replace our current FP-QCL. To obtain broad tunability, the QCL is placed in an external cavity system, giving over 100 cm-1 of frequency coverage near 8.5 microns. Our current laser only gives us ~20 cm-1 We plan to use this laser system to continue our attempts to observe C60 and to observe mid-IR vibrational modes of molecular ions, such as CH5+ and H5+.

External cavity QCL system
The external cavity QCL system which is being developed in our lab.

Related Content

Papers

84 B. M. Gibson and B. J. McCall
"Tilt-tuned etalon locking for tunable laser stabilization"
Optics Letters (2015), 40, 2696-2698.
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80 J. T. Stewart, B. E. Brumfield, B. M. Gibson, and B. J. McCall
"Inefficient Vibrational Cooling of C60 in a Supersonic Expansion"
ISRN Physical Chemistry (2013), 2013, 675138.
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78 J. T. Stewart and B. J. McCall
"Rotationally-Resolved Spectroscopy of the Donor Bending Mode of (D2O)2"
Journal of Physical Chemistry A (2013), 117, 13491–13499.
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73 J. T. Stewart and B. J. McCall
"Additional Bands of the Ar–D2O Intramolecular Bending Mode Observed Using a Quantum Cascade Laser"
Journal of Molecular Spectroscopy (2012), 282, 34-38.
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66 B. E. Brumfield, J. T. Stewart, and B. J. McCall
"Extending the Limits of Rotationally Resolved Absorption Spectroscopy: Pyrene"
Journal of Physical Chemistry Letters (2012), 3, 1985-1988.
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58 B. E. Brumfield, J. T. Stewart, and B. J. McCall
"High-Resolution Spectroscopy of the ν8 Band of Methylene Bromide Using a Quantum Cascade Laser"
Journal of Molecular Spectroscopy (2011), 266, 57-62.
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49 B. E. Brumfield, J. T. Stewart, S. L. Widicus Weaver, M. D. Escarra, S. S. Howard, C. F. Gmachl, and B. J. McCall
"A Quantum Cascade Laser cw Cavity Ringdown Spectrometer Coupled to a Supersonic Expansion Source"
Review of Scientific Instruments (2010), 81, 063102.
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Proceedings

13 S. L. Widicus Weaver, B. E. Brumfield, S. Howard, C. Gmachl and B. J. McCall
"A Laboratory and Observational Search for the Vibrational Spectrum of C60"
Proceedings of International Conference on Molecules in Space and Laboratory, Eds. J. L. Lemaire and F. Combes, (2007), 1-4.
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Talks

123 B. M. Gibson and B. J. McCall
"Development of a Frequency-Stabilized Mid-Infrared External Cavity-QCL Cavity Ringdown Spectrometer"
Sixty-Ninth International Symposium on Molecular Spectroscopy, University of Illinois, Urbana-Champaign, IL, 2014.
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124 B. M. Gibson, N. C. Koeppen, and B. J. McCall
"High-Resolution Spectroscopy of the ν16 Band of 1,3,5-Trioxane"
Sixty-Ninth International Symposium on Molecular Spectroscopy, University of Illinois, Urbana-Champaign, IL, 2014.
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117 J. T. Stewart, B. M. Gibson, and B. J. McCall
"Development of an External Cavity Quantum Cascade Laser for High-Resolution Spectroscopy of Molecular Ions"
Sixty-Eighth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2013.
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118 B. M. Gibson, J. T. Stewart, and B. J. McCall
"Development of a Sheath-Flow Supercritical Fluid Expansion Source for Vaporization of Nonvolatiles at Moderate Temperatures"
Sixty-Eighth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2013.
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114 J. T. Stewart and B. J. McCall
"Rotationally-Resolved Spectroscopy of the Bending Modes of Deuterated Water Dimer"
Sixty-Eighth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2013.
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112 B. M. Gibson, J. T. Stewart, B. E. Brumfield and B. J. McCall
"Vibrational Cooling of Large Molecules in Supersonic Expansions: The Case of C60 and Pyrene"
Sixty-Seventh International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2012.
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108 J. T. Stewart, B. M. Gibson and B. J. McCall
"Analysis of the High-Resolution Mid-Infrared Spectrum of Deuterated Water Clusters"
Sixty-Seventh International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2012.
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100 J. T. Stewart, B. E. Brumfield and B. J. McCall
"Rotationally-resolved Infrared Spectroscopy of the Polycyclic Aromatic Hydrocarbon Pyrene (C16H10) Using a Quantum Cascade Laser-based Cavity Ringdown Spectrometer"
Sixty-Sixth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2011.
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96 J. T. Stewart, B. E. Brumfield and B. J. McCall
"High-resolution Mid-infrared Spectroscopy of Deuterated Water Clusters Using a Quantum Cascade Laser-based Cavity Ringdown Spectrometer"
Sixty-Sixth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2011.
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82 J. T. Stewart, B. E. Brumfield, M. D. Escarra, C. F. Gmachl and B. J. McCall
"High-Resolution Spectroscopy of the ν8 Band of Methylene Bromide Using a Quantum Cascade Laser-Based Cavity Ringdown Spectrometer"
Sixty-Fifth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2010.
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73 B. E. Brumfield, J. T. Stewart, M. D. Escarra, C. F. Gmachl and B. J. McCall
"Astrochemistry and Spectroscopy of C60: The search for the 8.5 μm Vibrational Band"
239th American Chemical Society National Meeting, San Francisco, CA, 2010.
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69 B. E. Brumfield, J. T. Stewart, M. D. Escarra, C. Gmachl and B. J. McCall
"The Influence of Free-Running FP-QCL Frequency Jitter on Cavity Ringdown Spectroscopy of C60"
Sixty-Fourth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2009.
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53 B. E. Brumfield, S. S. Howard, C. F. Gmachl, D. K. Wilson, M. Percevault, and B. J. McCalll
"Development and Implementation of Optical Isolation for a Continuous Wave Fabry Perot Quantum Cascade Laser (CW-FP-QCL) at 8.5 um Using an Experimental Faraday Rotator"
Sixty-Third International Symposium on Molecular Spectroscopy, Ohio State University, Columbus, OH, 2008.
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40 S. L. Widicus Weaver, B. E. Brumfield, A. A. Mills, S. S. Howard, C. F. Gmachl, and B. J. McCall
"A Search for the 8.5 Micron Vibrational Spectrum of C60 in the Laboratory and Space"
Sixty-Second International Symposium on Molecular Spectroscopy, Ohio State University, Columbus, OH, 2007.
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39 B. E. Brumfield, S. L. Widicus Weaver, S. S. Howard, C. F. Gmachl, and B. J. McCall
"Cavity Ringdown Spectrum of the v8 Band of Methylene Bromide Using a Quantum Cascade Laser"
Sixty-Second International Symposium on Molecular Spectroscopy, Ohio State University, Columbus, OH, 2007.
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32 S. L. Widicus Weaver, B. E. Brumfield, S. Howard, C. Gmachl, and B. J. McCall
"A Laboratory and Observational Search for the Vibrational Spectrum of C60"
Molecules in Space and Laboratory, Paris, France, 2007.
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29 S. L. Widicus Weaver, M. C. Zwier, Y. Ding, and B. J. McCall
"Laboratory and Observational Studies of C60 and C60+"
American Chemical Society National Meeting, Atlanta, Georgia, 2006.
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Posters

32 N. C. Koeppen and B. J. McCall
"Analysis of rotationally resolved C3 using updated oscillator strengths"
Midwest Astrochemistry Meeting, The University of Northern Iowa, Cedar Falls, IA, 2015.
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25 J. T. Stewart, B. E. Brumfield and B. J. McCall
"Rotationally-Resolved Infrared Spectroscopy of the Polycyclic Aromatic Hydrocarbon Pyrene (C16H10)"
Midwest Astrochemistry Meeting, University of Illinois, Urbana, IL, 2011.
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21 B. E. Brumfield, J. T. Stewart and B. J. McCall
"Continued Development of a Sensitive Mid-IR Cavity Ring-down Spectrometer Using a Quantum Cascade Laser"
Midwest Astrochemistry Meeting, University of Illinois, Urbana, IL, 2010.
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15 B. E. Brumfield, J. T. Stewart and B. J. McCall
"Mid Infrared Continuous Wave Cavity Ringdown Spectrometer for Acquisition of the High-Resolution Spectrum of C60"
Second Midwest Astrochemistry Meeting, University of Illinois, 2009.
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10 B. E. Brumfield, B. Siller and B. J. McCall
"Towards Acquisition of a High Resolution Gas Phase Spectrum of C60"
Inaugural Midwest Astrochemistry Meeting, University of Illinois, 2008.
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5 B. E. Brumfield, S. L. Widicus Weaver, S. S. Howard, C. F. Gmachl, and B. J. McCall
"Continuous Wave Cavity Ringdown Spectroscopy of C60 at 8.5 Microns Using a Quantum Cascade Laser and a Supersonic Expansion Source"
American Chemical Society National Meeting, Chicago, Illinois, 2007.
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Other Publications

43 N. C. Koeppen
"High-resolution spectroscopic studies of carbon-containing species"
M. S. Thesis, University of Illinois, 2016.
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40 B. M. Gibson
"High-Resolution Infrared Spectroscopy in Pursuit of C60 and Other Astrochemical Targets"
Ph.D Thesis, University of Illinois, 2015.
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37 N. C. Koeppen, B. M. Gibson and B. J. McCall
"Progress towards a rotationally-resolved spectrum of C60"
AstroPAH In Focus, Issue 22, 2015.
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34 J. T. Stewart
"High-Resolution Infrared Spectroscopy of Large Molecules and Water Clusters Using Quantum Cascade Lasers"
Ph.D Thesis, University of Illinois, 2013.
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32 B. M. Gibson
"Design of a Supercritical Fluid Expansion Source for Gas-Phse Spectroscopy of Fullerenes"
Research Prospectus for Preliminary Examination, University of Illinois, 2013.
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26 B. E. Brumfield
"Development of a Quantum Cascade Laser Based Spectrometer for High Resolution Spectroscopy of Gas Phase C60"
Ph.D. Thesis, University of Illinois, 2011.
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25 J. T. Stewart
"High-Resolution Gas Phase Infrared Spectroscopy of Water Clusters and Cluster Ions Using Quantum Cascade Lasers"
Research Prospectus for Preliminary Examination, University of Illinois, 2011.
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14 B. E. Brumfield
"High-Resolution Spectroscopic Studies of C60 and C6H7+: Molecules of Fundamental Spectroscopic and Astrochemical Importance"
Research Prospectus for Preliminary Examination, University of Illinois, 2007.
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