Assistant Professor

Contact Info

Office:
177D
Phone Number:
Research Areas:
Research Interests:

          The Reber lab uses fiber-laser frequency combs to do ultrafast chemistry. Ultrafast spectroscopy is used for real-time tracking of dynamics in quantum mechanical systems on the femtosecond (10-15s) timescale. We employ a newly-developed technique called Cavity-Enhanced Transient Absorption Spectroscopy to increase the sensitivity of ultrafast absorption spectroscopy. We use ultrafast fiber-laser frequency combs and couple them to external enhancement cavities to both increase the power and effective absorption pathlength, thus giving signal enhancements of several orders of magnitude over traditional transient absorption spectroscopy. This technique allows us to study samples in molecular beams on the femtosecond timescale with transient absorption spectroscopy. Before the development of this technique, ultrafast transient absorption was limited to concentrated condensed phase samples and study of gas phase samples generally required an indirect probe, such as measuring the energy of an ejected electron, or was limited to molecules and states that fluoresce. Now, not only can we now do the same experiment on condense phase molecules as gas phase molecules via transient absorption spectroscopy, we are able to directly probe the molecular states undergoing the dynamics we wish to study.

          We are currently building up the fiber lasers and cavity-enhanced transient absorption spectrometer with unique frequency tuning capabilities. We will combine this with a molecular beam source to create a relatively cold source of molecules and the ability to make clusters, radicals, and other designer molecules. One research direction will study the fundamentals of light-harvesting molecules, with a focus on the process of singlet fission, in which one absorbed photon becomes two excited electrons. Single fission is already starting to be used to increase the efficiency of solar cells, even though it is not well understood. We aim to look at model systems and understand the fundamental mechanisms of singlet fission. A second direction of research will be to study ultrafast dynamics of combustion radicals. Eventually we will make infrared light to look at ultrafast vibrational dynamics in a wide range of molecular systems.

          Cavity-Enhanced Transient Absorption Spectroscopy is widely applicable as an ultrafast technique since it requires nothing more than an absorbing state to probe any ultrafast dynamics. By combining a large wavelength tuning range, we can probe many systems from UV-vis photochemistry to ultrafast vibrational dynamics in the IR. With a molecular beam we can study not just stable compounds, but can make designer molecules (such as clusters) and short-lived molecules (such as radicals) and can study those as well. Additionally, the instrument is general enough to be able to do multidimensional spectroscopy with only a few small modifications.

Selected Publications:

X. L. Li, M. A. R. Reber, C. Corder, Y. Chen, P. Zhao, T. K. Allison. High-power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools. Rev. Sci. Inst. 2016; 87: 093114.

M. A. Roberts Reber, Y. Chen, and T. K. Allison. Cavity-enhanced ultrafast spectroscopy: ultrafast meets ultrasensitive. Optica 2016; 3:311.

M. A. Roberts, E. N. Sharp-Williams, and D. J. Nesbitt. High-resolution direct-absorption spectroscopy of hydroxymethyl radical in the CH symmetric stretching region. J. Phys. Chem. A. 2013; 117:7042-7049.

M. A. Roberts, C. Savage, F. Dong, E. N. Sharp-Williams, A. B. McCoy, and D. J. Nesbitt. Sub-Doppler infrared spectroscopy of CH2D radical in a slit supersonic jet: Isotopic symmetry breaking in the CH stretching manifold. J. Chem. Phys. 2012; 136:234308.

E. N. Sharp-Williams, M. A. Roberts, and D. J. Nesbitt. Dark state vibronic coupling in the A2Π-X2Σ+ band of ethynyl radical via high resolution infrared absorption spectroscopy. Phys. Chem. Chem. Phys. 2011; 13:17474-17483.

E. N. Sharp-Williams, M. A. Roberts, and D. J. Nesbitt. High resolution slit-jet infrared spectroscopy of ethynyl radical: 2Π-2Σ+ vibronic bands with sub-Doppler resolution. J. Chem. Phys. 2011; 134:064314.

E. N. Sharp, M. A. Roberts, and D.J. Nesbitt. Rotationally resolved infrared spectroscopy of jet-cooled phenyl radical in the gas phase. Phys. Chem. Chem. Phys. 2008; 10:6592-6596. cover art

F. Dong, M. Roberts, and D. J. Nesbitt. High-resolution infrared spectroscopy of jet cooled vinyl radical: symmetric CH2 stretch excitation and tunneling dynamics. J. Chem. Phys. 2008; 128:044305.

D. J. Nesbitt, E. S. Whitney, M. Roberts, and C. Savage. Spectroscopy in slit supersonic jet discharges: fine and hyperfine structure calculations for asymmetric top radicals with multiple nuclear spins. Molecular Physics 2007; 105:467-475. J. M. Brown special issue invited paper

M. A. Roberts, C. G. Alfonzo, K. J. Manke, W. M. Ames, D. B. Ron, and T. D. Varberg. Hyperfine structure in the electronic spectrum of ReO. Molecular Physics 2007; 105:917-921. J. M. Brown special issue invited paper

Reber, M. A. (2017). A Symphony of Light: Using lasers and resonators to study ultrafast chemistry. In Herty Medalist Undergraduate Research Symposium. Morehouse College, Atlanta, GA.

Reber, M. A., & Cooper, N. (2017). Cavity-enhanced transient absorption spectroscopy of species in molecular beams. Poster session presented at the meeting of  Time Resolved Vibrational Spectroscopy Conference.

Reber, M. A., Allison, T. K., & Chen, Y. (2016). Cavity-enhanced ultrafast spectroscopy: ultrafast meets ultrasensitive. In International Symposium on Molecular Spectroscopy.

Li, X., Reber, M. A. R., Corder, C., Chen, Y., Zhao, P., & Allison, T. K. (2016). High-power ultrafast Yb: fiber laser frequency combs using commercially available components and basic fiber tools. Review of Scientific Instruments, 87(9), 093114.

Reber, M. A. R., Chen, Y., & Allison, T. K. (2016). Cavity-enhanced ultrafast spectroscopy: ultrafast meets ultrasensitive. Optica, 3(3), 311-317.

Li, X., Zhao, P., Corder, C., Polanco, A., Reber, M., Chen, Y., . . . Allison, T. (2015). Real-time Dynamics of Surface Photoreactions Probed with Ultrashort XUV Pulses. In APS Division of Atomic, Molecular and Optical Physics Meeting Abstracts Vol. 1 (pp. 1107).

Reber, M. A. R., Chen, Y., & Allison, T. K. (2015). Cavity-Enhanced Ultrafast Transient Absorption Spectroscopy. arXiv preprint arXiv:1511.02973.

Allison, T. K., Reber, M. R., & Chen, Y. (2015). Cavity Enhanced Ultrafast Transient Absorption Spectroscopy. In 70th International Symposium on Molecular Spectroscopy Vol. 1.

Chen, Y., Reber, M. R., Keleher, K., & Allison, T. K. (2014). Cavity-Enhanced Ultrafast Transient Absorption Spectroscopy. In 69th International Symposium on Molecular Spectroscopy Vol. 1.

Chang, C., Roberts, M. A., & Nesbitt, D. J. (2013). Sub-Doppler Slit Jet Discharge Spectroscopy of Jet Cooled Polyacetylenes: the Anti-Symmetric CH Stretch Mode of Triacetylene. In 68th International Symposium on Molecular Spectroscopy Vol. 1.

Chang, C., Roberts, M. A., & Nesbitt, D. J. (2013). Slit-Jet Discharge Studies of Polyacetylenic Molecules: Synthesis and High Resolution Infrared Spectroscopy of Diacetylene. In 68th International Symposium on Molecular Spectroscopy Vol. 1.

Roberts, M. A., Sharp-Williams, E. N., & Nesbitt, D. J. (2013). High-Resolution Direct-Absorption Spectroscopy of Hydroxymethyl Radical in the CH Symmetric Stretching Region. The Journal of Physical Chemistry A, 117(32), 7042-7049. doi:10.1021/jp312877k

Roberts, M. A., Savage, C., Dong, F., Sharp-Williams, E. N., McCoy, A. B., & Nesbitt, D. J. (2012). Sub-Doppler infrared spectroscopy of CH2D radical in a slit supersonic jet: Isotopic symmetry breaking in the CH stretching manifold. The Journal of chemical physics, 136(23), 234308.

Roberts, M. A. (2012). High Resolution Infrared Spectroscopy of Slit-Jet Cooled Radicals and Ions. University of Colorado.

Sharp-Williams, E. N., Roberts, M. A., & Nesbitt, D. J. (2011). Publisher's Note. Journal of Chemical Physics, 134(15), 9901.

Roberts, M. A., Nesbitt, D. J., & McCoy, A. B. (2011). Modeling Vibrational Structure Using Harmonically-Coupled Morse Oscillators: a Global Description of the CH Stretches in Methyl Radical and its Deuterated Isotopomers. In 66th International Symposium On Molecular Spectroscopy Vol. 1.

Sharp-Williams, E. N., Roberts, M. A., & Nesbitt, D. J. (2011). High resolution slit-jet infrared spectroscopy of ethynyl radical: 2Π–2Σ+ vibronic bands with sub-Doppler resolution. The Journal of chemical physics, 134(6), 064314.

Sharp-Williams, E. N., Roberts, M. A., & Nesbitt, D. J. (2011). Dark state vibronic coupling in the à (2 Π)← X [combining tilde](2 Σ+) band of ethynyl radical via high resolution infrared absorption spectroscopy. Physical Chemistry Chemical Physics, 13(39), 17474-17483.

Sharp-Williams, E. N., Roberts, M. A., & Nesbitt, D. J. (2011). Dark state vibronic coupling in the A (2 [capital Pi])?[X with combining tilde](2 [capital Sigma]+) band of ethynyl radical via high resolution infrared absorption spectroscopy. Physical Chemistry Chemical Physics, 13(39), 17474-17483.

Sharp-Williams, E., Roberts, M. A., Roscioli, J. R., Gisler, A. W., Ziemkiewicz, M., Nesbitt, D. J., . . . Perkins Jr, B. G. (2010). High Resolution Spectroscopy and Dynamics: from Jet Cooled Radicals to Gas-Liquid Interfaces. In 65th International Symposium On Molecular Spectroscopy Vol. 1.

Sharp-Williams, E. N., Roberts, M. A., Nesbitt, D. J., & Curl, R. F. (2009). Reinvestigating the tilde {A}-tilde {X} Spectrum of Ethynyl Radical: New Insights Into the Spectroscopy of^ 2Pi-^ 2Sigma^+ Vibronic Bands. In 64th International Symposium On Molecular Spectroscopy Vol. 1.

Sharp-Williams, E. N., Roberts, M. A., & Nesbitt, D. J. (2009). High Resolution Infrared Spectroscopy of Jet-Cooled Phenyl Radical in the Gas Phase. In 64th International Symposium On Molecular Spectroscopy Vol. 1.

Roberts, M. A., Sharp-Williams, E. N., & Nesbitt, D. J. (2009). High Resolution Direct Absorption Spectroscopy of Hydroxymethyl Radical in the Mid-Infrared. In 64th International Symposium On Molecular Spectroscopy Vol. 1.

Roberts, M. A., Savage, C., Dong, F., & Nesbitt, D. J. (2009). Fine and Hyperfine Structure in Sub-Doppler Infrared, Ch-Stretching Spectra of Monodeuterated Methyl Radical. In 64th International Symposium On Molecular Spectroscopy Vol. 1.

Dong, F., Roberts, M. A., & Nesbitt, D. J. (2008). Toward an Ab Initio Understanding of Quantum Tunneling Dynamics in Vinyl Radical: A Vibrationally Adiabatic Approach.

Sharp, E. N., Roberts, M. A., & Nesbitt, D. J. (2008). Rotationally resolved infrared spectroscopy of a jet-cooled phenyl radical in the gas phase. Physical Chemistry Chemical Physics, 10(44), 6592-6596.

Nesbitt, D. J., Dong, F., Roberts, M., Zolot, A., & Ziemkiewicz, M. (2008). PHYS 72-Spectroscopy and reaction dynamics of open-shell species: A quantum state resolved perspective. In ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY Vol. 235. AMER CHEMICAL SOC 1155 16TH ST, NW, WASHINGTON, DC 20036 USA.

Dong, F., Roberts, M., & Nesbitt, D. J. (2008). High-resolution infrared spectroscopy of jet-cooled vinyl radical: Symmetric CH2 stretch excitation and tunneling dynamics. The Journal of chemical physics, 128(4), 044305.

Roberts, M. A., Walters, R. S., & Nesbitt, D. J. (2008). FIRST HIGH RESOLUTION INFRARED SPECTROSCOPY OF GAS PHASE CYCLOPENTYL RADICAL: STRUCTURAL AND DYNAMICAL INSIGHTS FROM THE LONE CH STRETCH REGION.

Nesbitt, D. J., Whitney**, E. S., Roberts, M., & Savage***, C. (2007). Spectroscopy in slit supersonic jet discharges: fine and hyperfine structure calculations for asymmetric top radicals with multiple nuclear spins. Molecular Physics, 105(5-7), 467-475. doi:10.1080/00268970601153381

Roberts, M. A., Savage, C., Walters, R. S., & Nesbitt, D. J. (2007). MICROSLIT INJECTORS IN A SUPERSONIC SLIT JET EXPANSION: A NEW TOOL FOR RADICAL SYNTHESIS AND KINETICS.

Varberg, T., Roberts, M. A., Alfonzo, C. G., & Manke, K. J. (2007). Hyperfine Structure in the Electronic Spectrum of ReO. Molecular Physics, 105.

Roberts, M. A., Alfonzo, C. G., Manke, K. J., Ames, W. M., Ron, D. B., & Varberg, T. D. (2007). Hyperfine structure in the electronic spectrum of ReO. Molecular Physics, 105(5-7), 917-921. doi:10.1080/00268970601075295

Dong, F., Roberts, M. A., Walters, R. S., & Nesbitt, D. J. (2007). CH Stretch Vibrational Spectroscopy and Tunneling Dynamics in Vinyl Radical.

Roberts, M. E. L. A. N. I. E. A., Savage, C., & Nesbitt, D. J. (2006). HIGH RESOLUTION INFRARED SPECTROSCOPY OF CH $ _2 $ D.

X. L. Li, M. A. R. Reber, C. Corder, Y. Chen, P. Zhao, T. K. Allison. High-Power ultrafast Yb:fiber laser frequency combs using commercially available components and basic fiber tools. Submitted June, 2016. (arXiv:1606.05234)

M. A. Roberts Reber, Y. Chen, and T. K. Allison. Cavity-enhanced ultrafast spectroscopy: ultrafast meets ultrasensitive. Optica. 2016; 3:311-317.

M. A. Roberts, E. N. Sharp-Williams, and D. J. Nesbitt. High-resolution direct-absorption spectroscopy of hydroxymethyl radical in the CH symmetric stretching region. J. Phys. Chem. A. 2013; 117:7042-7049.

M. A. Roberts, C. Savage, F. Dong, E. N. Sharp-Williams, A. B. McCoy, and D. J. Nesbitt. Sub-Doppler infrared spectroscopy of CH2D radical in a slit supersonic jet: Isotopic symmetry breaking in the CH stretching manifold. J. Chem. Phys. 2012; 136:234308.

E. N. Sharp-Williams, M. A. Roberts, and D. J. Nesbitt. Dark state vibronic coupling in the A2Π-X2Σ+ band of ethynyl radical via high resolution infrared absorption spectroscopy.  Phys. Chem. Chem. Phys. 2011; 13:17474-17483.

E. N. Sharp-Williams, M. A. Roberts, and D. J. Nesbitt. High resolution slit-jet infrared spectroscopy of ethynyl radical: 2Π-2Σ+ vibronic bands with sub-Doppler resolution. J. Chem. Phys. 2011; 134:064314.

E. N. Sharp, M. A. Roberts, and D.J. Nesbitt. Rotationally resolved infrared spectroscopy of jet-cooled phenyl radical in the gas phase. Phys. Chem. Chem. Phys. 2008; 10:6592-6596. cover art

F. Dong, M. Roberts, and D. J. Nesbitt. High-resolution infrared spectroscopy of jet cooled vinyl radical: symmetric CH2 stretch excitation and tunneling dynamics. J. Chem. Phys. 2008; 128:044305.

D. J. Nesbitt, E. S. Whitney, M. Roberts, and C. Savage. Spectroscopy in slit supersonic jet discharges: fine and hyperfine structure calculations for asymmetric top radicals with multiple nuclear spins. Molecular Physics 2007; 105:467-475. J. M. Brown special issue invited paper

M. A. Roberts, C. G. Alfonzo, K. J. Manke, W. M. Ames, D. B. Ron, and T. D. Varberg. Hyperfine structure in the electronic spectrum of ReO. Molecular Physics 2007; 105:917-921. J. M. Brown special issue invited paper