NEWS
VANADIUM HYDRIDE
august 2022
I just published the first detection and analysis of an electronic spectrum of vanadium hydride (VH). This is the last of the 3d transition metal monohydrides for which there are no reported spectra. Several metal hydrides have been found in the photospheres of cooler stars within our Galaxy, so we hope an astronomer will be inspired to look for VH now that an electronic band has been recorded and analyzed.
NSF RENEWAL
AUGUST 2021
The National Science Foundation has fully funded my Research in Undergraduate Institutions (RUI) renewal proposal in the CSDM-A program of the Division of Chemistry. This three-year grant, entitled “Electronic Spectroscopy of Vanadium Hydride and Niobium Hydride” will run through July 2024, enabling me to hire another generation of talented Macalester students who want to receive training in experimental physical chemistry and chemical physics. I am very grateful to the NSF for this critical support.
Honoring Anthony merer
July 2020
I presented our recent work on the electronic spectroscopy of tantalum hydride (TaH) at the 25th International Conference on High Resolution Molecular Spectroscopy at Bilbao, Spain. My co-authors are Sam Gleason, Paul Reischmann and Dalir Kellett. This work has now been published in a special issue of the Journal of Molecular Spectroscopy honoring Anthony Merer, who is a long-time collaborator of mine and an inspiration to all spectroscopists.
Tom Varberg
DeWitt Wallace Professor of Chemistry
I have been teaching Physical and General Chemistry at Macalester College since 1993. My research is focused on the electronic spectroscopy of metal-containing free radicals in the gas phase, particularly their fine and hyperfine structures. We utilize pulsed and continuous-wave lasers (both dye and Ti:sapphire), often working at very high resolution. We seek to unravel and assign the complicated spectra of these open-shell free radicals, thus deciphering their Hamiltonians and illuminating their electronic structure. Some of these molecules are of astronomical interest, as this image of the Orion Molecular Cloud Complex suggests.
I received my B.A. degree in chemistry in 1985 from Hamline University and my Ph.D. degree in physical chemistry from MIT in 1990. I was a postdoctoral scholar at the National Institute of Standards and Technology from 1990–92 and a NATO Postdoctoral Fellow at the University of Oxford from 1992–93. In this training, I explored the spectroscopy of free radicals using a variety of experimental techniques and wavelengths (microwave, far-infrared and visible).
I have had five sabbatical leaves from Macalester College, taken in (1) Boulder, Colorado, (2) Vancouver, British Columbia, (3) Sydney, Australia, (4) Zürich, Switzerland & Florence, Italy, and (5) Cape Town, South Africa, Bologna, Italy & London, England, as well as two research summers spent at the University of Oxford, England.
I take as my professional motto the sentiment expressed by the 19th-century French chemist and statesman Jean-Baptiste Dumas, who once wrote that “the greatest joy of my life has been to accomplish original scientific work, and next to that, to lecture to a group of intelligent students.“ I feel fortunate to be able to do the same here at Macalester College.
RECENT RESEARCH PROJECTS
We have recently recorded two electronic transitions in the previously unreported gas-phase molecule vanadium hydride. The first of these bands, that of the D5Pi–X5Delta (0,0) band at 654 nm, has now been published in the Journal of Chemical Physics. Both states rapidly spin uncouple from Hund's case (a) to case (b), which made the spectrum an interesting challenge to unravel and assign. We have recorded another transition further to the red which is still being analyzed. Work on VH and VD will continue in the summer of 2023 with new student collaborators.
We have recorded and analyzed (one last!) band of a favorite molecule of ours, TaO. This spectrum is of the D2Pi–X2Delta (0,0) transition near 696 nm, which had been previously detected by other workers but never assigned or analyzed. The band has fearsome hyperfine structure, as seen in the figure, which shows the eight-fold splitting by the I = 7/2 spin of the 181Ta nucleus. At the Doppler-limited resolution of our experiment, there were many overlapping lines, but in the final analysis we were able to assign essentially every feature in the spectrum. My collaborator in this work is Kevin Tovar ('23).
I have developed a laboratory experiment for a Quantum Chemistry course in which students record the Raman spectrum of para-difluorobenzene and then use group theory and computational chemistry to assign all of the observed Stokes lines. An innovative feature is the assignment of several overtone and combination bands in the dense spectrum of this organic molecule.
We have worked hard for a few years now on the challenging electronic spectrum of tantalum hydride (TaH). My collaborators on this project include Siddhant Singh, Zach Fried, Sam Gleason, Paul Reischmann, Dalir Kellett, Stephanie Lee and Casey Christopher. The molecule displays ferocious homogeneous (spin-orbit) and heterogeneous (rotational) perturbations, but we have made good progress. The figure shows all of the electronic states we have identified, including six low-lying states within 0.5 eV of each other, as determined from a combination of laser excitation and dispersed fluorescence experiments.
We were the first to study the electronic spectrum of the molecule gold sulfide, AuS. The gold–sulfur bond is of fundamental interest in the nanoelectronics and molecular self-assembly communities. We have analyzed transitions from the ²Π ground state to three excited doublet states and a low-lying quartet state, all at hyperfine resolution. This work has been carried out by several students, including Austin Parsons, Sam Gleason, Brad Pearlman, Ian Wyse and Kaarin Evens and has led to three publications. We have also collaborated with Tim Steimle's group at ASU on this work.
We have recently developed new laboratory exercises for the undergraduate physical chemistry lab, published as three different articles in the Journal of Chemical Education. These experiments comprise powder x-ray diffractometry, acoustic interferometry with an Apple iPad, and the measurement of gas compressibilities. Collaborators include research students Andrew Bendelsmith, Kacper Skakuj, Brad Pearlman, Ian Wyse, Sam Gleason and Dalir Kellett as well as my colleagues Keith Kuwata and Ken Moffett.
Tantalum oxide has been a favorite molecule of ours. We have published two studies on TaO, with a particular focus on the hyperfine structures of the ground and several excited states. Macalester students Kara Manke, Tyson Vervoort, Casey Christopher, Stephanie Lee, Francis Gwandu, Andrew Matsumoto, Ben Knurr, Tom Mahle and Zachary Morrow have all worked on this interesting molecule.
Our interest in gold chemistry and spectroscopy first began by recording unbelievably strong spectra of gold fluoride in the visible region, made from the reaction of sputtered gold with sulfur hexafluoride. The molecule produced beautiful “textbook” spectra such as the one shown here. By recording Doppler-free spectra we were able to resolve and analyze hyperfine splittings from both the Au and F nuclei. This work was carried out by Ben Knurr, Elissa Butler, Kara Manke and Tyson Vervoort.
Macalester student Andrew Bendelsmith and I analyzed two electronic bands of tantalum sulfide (TaS) at high resolution in order to understand the hyperfine structure of the molecule. As you can see in this sub-Doppler spectrum, the spin of the Ta nucleus is 7/2 producing eight hyperfine components. My colleague Keith Kuwata used density functional theory to obtain values of the magnetic hyperfine parameters that are in excellent agreement with our experimental results.
FUNDING
The Varberg research group is grateful to the following funding agencies for support of the work in our lab.
2021–2024
$ 264,328
National Science Foundation
RUI Grant
2016–2020
$ 223,682
National Science Foundation
RUI Grant
2013–2016
$ 213,447
National Science Foundation
RUI Grant
2009–2013
$ 230,560
National Science Foundation
RUI Grant
2007–2008
$ 50,000
ACS Petroleum Research Fund
UFS Grant
2005–2009
$ 228,406
National Science Foundation
RUI Grant
2005–2006
$ 147,537
National Science Foundation
MRI Grant (with co-PIs)
2002–2005
$ 211,209
National Science Foundation
MRI Grant
1998–2003
$ 60,000
Dreyfus Foundation
Henry Dreyfus Teacher–Scholar Award
1996–1998
$ 11,269
National Science Foundation
ILI Grant (with co-PIs)
1995–1999
$ 20,000
ACS Petroleum Research Fund
Type G Grant
1994–1996
$ 32,000
Research Corporation
Cottrell College Science Award
1992–1993
$ 41,000
National Science Foundation
NATO Postdoctoral Fellowship
2022
42. T. D. Varberg, “First detection and analysis of an electronic spectrum of vanadium hydride: The D⁵Π–X⁵Δ (0,0) band,” Journal of Chemical Physics, 2022, 157, 074311.
Article
41. K. A. Tovar* and T. D. Varberg, “Rotational and hyperfine analysis of the D²Π₁⸝₂ –X²Δ₃⸝₂ (0,0) band of TaO,” Journal of Molecular Spectroscopy, 2022, 387, 111666.
Article
40. T. D. Varberg, "Raman spectroscopy, group theory, and computational chemistry: A physical chemistry laboratory experiment on para-difluorobenzene," Journal of Chemical Education, 2022, 99, 2129–2134.
Article
2020
39. Z. T. P. Fried*, S. Singh*and T. D. Varberg,“Connecting all electronic states of TaH: Observation of five new weak bands,” Journal of Molecular Spectroscopy, 2020, 372, 111332.
Article | Supplementary Data
38. B. W. Pearlman*, I. A. Wyse*, K. K. Evens* and T. D. Varberg, “Rotational and hyperfine analysis of the A²Σ⁺–X₁²Π₃⸝₂ and B²Σ⁻–X₁²Π₃⸝₂ transitions of AuS,” Molecular Physics, 2020, 118, e1689305.
Article | Supplementary Data
2019
37. S. P. Gleason*, D. H. P. Kellett*, P. P. Reischmann* and T. D. Varberg, “The red bands of TaH: Identification of the ground and low-lying electronic states,” Journal of Molecular Spectroscopy, 2019, 362, 56–60.
Article | Supplementary Data
2018
36. A. J. Parsons*, S. P. Gleason* and T. D. Varberg, “High resolution spectroscopy of the a⁴Σ⁻₃⸝₂–X₁²Π₃⸝₂ system of gold monosulphide in the near infrared,” Molecular Physics, 2018, 116, 3547–3553.
Article
2017
35. T. D. Varberg, B. W. Pearlman*, I. A. Wyse*, S. P. Gleason*, D. H. P. Kellett* and K. L. Moffett, “Determining the speed of sound and heat capacity ratios of gases by acoustic interferometry,” Journal of Chemical Education, 2017, 94, 1995–1998.
Article
2015
34. D. L. Kokkin, R. Zhang, T. C. Steimle, I. A. Wyse*, B. W. Pearlman* and T. D. Varberg, “Au–S bonding revealed from the characterization of diatomic gold sulfide, AuS,” Journal of Physical Chemistry A, 2015, 119, 11659–11667.
Article | Supplementary Data
33. T. D. Varberg and K. Skakuj*, “X-ray diffraction of intermetallic compounds: A physical chemistry laboratory experiment,” Journal of Chemical Education, 2015, 92, 1095–1097.
Article | Supplementary Data
2014
32. C. R. Christopher*, S. Y. Lee*, F. B. Gwandu*, A. J. Matsumoto*, B. J. Knurr*, T. K. Mahle*, Z. W. Morrow* and T. D. Varberg, “Rotational and hyperfine analysis of the E²Π₁⸝₂–X²Δ₃⸝₂ electronic transition of TaO,“ Journal of Molecular Spectroscopy, 2014, 301, 25–27.
Article | Supplementary Data
31. S. Y. Lee*, C. R. Christopher*, K. J. Manke*, T. R. Vervoort* and T. D. Varberg, “The electronic spectrum of tantalum hydride and deuteride,” Molecular Physics, 2014,112, 2424–2432.
Article
2013
30. T. C. Steimle, R. Zhang, C. Qin and T. D. Varberg, “Molecular-beam optical Stark and Zeeman study of the [17.8]0⁺–X¹Σ⁺ band system of AuF,“ Journal of Physical Chemistry A, 2013, 117, 11737–11744.
Article
2012
29. A. J. Bendelsmith*, K. T. Kuwata and T. D. Varberg, “Hyperfine structure in the electronic spectrum of TaS,” Journal of Molecular Spectroscopy, 2012, 276–277, 14–18.
Article | Supplementary Data
2011
28. T. D. Varberg, A. J. Bendelsmith* and K. T. Kuwata, “Measurement of the compressibility factor of gases: A physical chemistry laboratory experiment,” Journal of Chemical Education, 2011, 88, 1166–1169.
Article
2010
27. E. K. Butler*, B. J. Knurr*, K. J. Manke*, T. R. Vervoort* and T. D. Varberg, “Excited electronic states of AuF,” Journal of Physical Chemistry A, 2010, 114, 4831–4834.
Article | Supplementary Data
2009
26. B. J. Knurr*, E. K. Butler* and T. D. Varberg, “Electronic spectrum of AuF: Hyperfine structure of the [17.7]1 state,” Journal of Physical Chemistry A, 2009, 113, 13428–13435.
Article
2008
25. D. L. Kokkin, T. P. Troy, M. Nakajima, K. Nauta, T. D. Varberg, G. F. Metha, N. T. Lucas and T. W. Schmidt, “The optical spectrum of a large isolated polycyclic aromatic hydrocarbon: hexa-peri-hexabenzocoronene, C₄₂H₁₈,” Astrophysical Journal, 2008, 681, L49–L51.
Article
24. K. J. Manke*, T. R. Vervoort*, K. T. Kuwata and T. D. Varberg, “Electronic spectrum of TaO and its hyperfine structure,” Journal of Chemical Physics, 2008, 128, 104302/1–6.
Article | Supplementary Data
2007
23. 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.
Article | Supplementary Data
2006
22. P. J. Hodges, J. M. Brown and T. D. Varberg, “The ultraviolet spectrum of the CoCl₂ radical, studied at vibrational and rotational resolution,” Journal of Chemical Physics, 2006, 124, 204302/1–10.
Article
21. A. Shayesteh, R. J. Le Roy, T. D. Varberg and P. F. Bernath, “Multi-isotopologue analyses of new vibration–rotation and pure rotation spectra of ZnH and CdH,” Journal of Molecular Spectroscopy, 2006, 237, 87–96.
Article | Supplementary Data
2004
20. T. D. Varberg and J. C. Roberts*, “The isotopic dependence of the spin–rotation interaction: The rotational spectrum of cadmium hydride in its X²Σ⁺ state,” Journal of Molecular Spectroscopy, 2004, 223, 1–8.
Article
2002
19. C. T. Kingston, A. J. Merer and T. D. Varberg, “The electronic spectrum of NiCN in the visible region,” Journal of Molecular Spectroscopy, 2002, 215, 106–127.
Article
1999
18. T. D. Varberg, F. Stroh and K. M. Evenson, “Far-infrared rotational and fine-structure transition frequencies and molecular constants of NO in the X²Π (v = 0) state,” Journal of Molecular Spectroscopy, 1999, 196, 5–13.
Article | Supplementary Data
1998
17. T. D. Varberg, J. C. Roberts*, K. A. Tuominen* and K. M. Evenson, “The far-infrared spectrum of deuterium iodide,” Journal of Molecular Spectroscopy, 1998, 191, 384–386.
Article
1997
16. F. A. Tezcan*, T. D. Varberg, F. Stroh and K. M. Evenson, “Far-infrared rotational spectra of ZnH and ZnD in the X²Σ⁺ (v = 0) state,” Journal of Molecular Spectroscopy, 1997, 185, 290–295.
Article
15. N. M. Lakin, T. D. Varberg and J. M. Brown, “The detection of lines in the microwave spectrum of indium hydroxide, InOH, and its isotopomers,” Journal of Molecular Spectroscopy, 1997, 183, 34–41.
Article
1995
14. M. Bellini, P. De Natale, M. Inguscio, T. D. Varberg and J. M. Brown, “Precise experimental test of models for the breakdown of the Born–Oppenheimer separation: The rotational spectra of isotopic variants of lithium hydride,” Physical Review A,1995, 52, 1954–1960.
Article
1994
13. R. J. Low, C. J. Whitham, T. D. Varberg and B. J. Howard, “The microwave spectrum of the open-shell complex Ar⋅NO₂,” Chemical Physics Letters, 1994, 222, 443–449.
Article
12. J. M. Brown, T. D. Varberg, K. M. Evenson and A. L. Cooksy, “The fine-structure intervals of N⁺ by far-infrared laser magnetic resonance,” Astrophysical Journal, 1994, 428, L37–L40.
Article
11. T. D. Varberg, K. M. Evenson and J. M. Brown, “Detection of OH⁺ in its a¹Δ state by far-infrared laser magnetic resonance,” Journal of Chemical Physics, 1994,100, 2487–2491.
Article
10. T. D. Varberg and K. M. Evenson, “The pure rotational spectra of CuH and CuD in their ground states measured by tunable far-infrared spectroscopy,” Journal of Molecular Spectroscopy, 1994, 164, 531–535.
Article
1993
9. K. V. Chance, T. D. Varberg, K. Park and L. R. Zink, “The far-infrared spectrum of HI,” Journal of Molecular Spectroscopy, 1993, 162, 120–126.
Article
8. R. J. Low, T. D. Varberg, J. P. Connelly, A. R. Auty, B. J. Howard and J. M. Brown, “The hyperfine structures of CuCl and CuBr in their ground states studied by microwave Fourier transform spectroscopy,” Journal of Molecular Spectroscopy, 1993, 161, 499–510.
Article
7. T. D. Varberg and K. M. Evenson, “Laser spectroscopy of carbon monoxide: A frequency reference for the far-infrared,” IEEE Transactions on Instrumentation and Measurement, 1993, 42, 412–414.
Article
6. T. D. Varberg and K. M. Evenson, “The rotational spectrum of OH in the v = 0–3 levels of its ground state,” Journal of Molecular Spectroscopy, 1993, 157, 55–67.
Article
1992
5. T. D. Varberg, J. A. Gray, R. W. Field and A. J. Merer, “Reanalysis and extension of the MnH A⁷Π–X⁷Σ⁺(0,0) band: Fine structure and hyperfine-induced rotational branches,” Journal of Molecular Spectroscopy, 1992, 156, 296–318.
Article
4. T. D. Varberg and K. M. Evenson, “Accurate far-infrared rotational frequencies of carbon monoxide,” Astrophysical Journal, 1992, 385, 763–765.
Article
1991
3. T. D. Varberg, R. W. Field and A. J. Merer, “Elucidation of electronic structure by the analysis of hyperfine interactions: The MnH A⁷Π–X⁷Σ⁺(0,0) band,” Journal of Chemical Physics, 1991, 95, 1563–1576.
Article
1990
2. T. D. Varberg, R. W. Field and A. J. Merer, “Hyperfine structure of the MnH X⁷Σ⁺state: A large gas-to-matrix shift in the Fermi contact interaction,” Journal of Chemical Physics, 1990, 92, 7123–7127.
Article
1989
1. T. D. Varberg, E. J. Hill and R. W. Field, “Laser spectroscopy of CoH: Spin–orbit splitting of the ground state,” Journal of Molecular Spectroscopy, 1989, 138, 630–637.
Article