Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Continuous probing of cold complex molecules with infrared frequency comb spectroscopy

Abstract

For more than half a century, high-resolution infrared spectroscopy has played a crucial role in probing molecular structure and dynamics. Such studies have so far been largely restricted to relatively small and simple systems, because at room temperature even molecules of modest size already occupy many millions of rotational/vibrational states, yielding highly congested spectra that are difficult to assign. Targeting more complex molecules requires methods that can record broadband infrared spectra (that is, spanning multiple vibrational bands) with both high resolution and high sensitivity. However, infrared spectroscopic techniques have hitherto been limited either by narrow bandwidth and long acquisition time1, or by low sensitivity and resolution2. Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) combines the inherent broad bandwidth and high resolution of an optical frequency comb with the high detection sensitivity provided by a high-finesse enhancement cavity3,4, but it still suffers from spectral congestion5. Here we show that this problem can be overcome by using buffer gas cooling6 to produce continuous, cold samples of molecules that are then subjected to CE-DFCS. This integration allows us to acquire a rotationally resolved direct absorption spectrum in the C–H stretching region of nitromethane, a model system that challenges our understanding of large-amplitude vibrational motion7,8,9. We have also used this technique on several large organic molecules that are of fundamental spectroscopic and astrochemical relevance, including naphthalene10, adamantane11 and hexamethylenetetramine12. These findings establish the value of our approach for studying much larger and more complex molecules than have been probed so far, enabling complex molecules and their kinetics to be studied with orders-of-magnitude improvements in efficiency, spectral resolution and specificity.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Buy article

Get time limited or full article access on ReadCube.

$32.00

All prices are NET prices.

Figure 1: Buffer gas cooling of nitromethane.
Figure 2: A schematic of the combined CE-DFCS and buffer gas cooling apparatus.
Figure 3: Survey absorption spectrum of nitromethane.
Figure 4: Survey absorption spectrum of several large molecules.

References

  1. Gagliardi, G. & Loock, H.-P. (eds) Cavity-Enhanced Spectroscopy and Sensing Chs 4–7 (Springer, 2014)

  2. Griffith, P. R. & Haseth, J. A. Fourier Transform Infrared Spectrometry (Wiley, 2007)

  3. Thorpe, M. J. et al. Broadband cavity ringdown spectroscopy for sensitive and rapid molecular detection. Science 311, 1595–1599 (2006)

    CAS  PubMed  Article  ADS  Google Scholar 

  4. Foltynowicz, A. et al. Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared application to trace detection of hydrogen peroxide. Appl. Phys. B 110, 163–175 (2013)

    CAS  Article  ADS  Google Scholar 

  5. Adler, F. et al. Mid-infrared Fourier transform spectroscopy with a broadband frequency comb. Opt. Express 18, 21861–21872 (2010)

    CAS  PubMed  Article  ADS  Google Scholar 

  6. Patterson, D., Tsikata, E. & Doyle, J. M. Cooling and collisions of large gas phase molecules. Phys. Chem. Chem. Phys. 12, 9736–9741 (2010)

    CAS  PubMed  Article  Google Scholar 

  7. Tannenbaum, E., Myers, R. J. & Gwinn, W. D. Microwave spectra, dipole moment, and barrier to internal rotation of CH3NO2 and CD3NO2 . J. Chem. Phys. 25, 42–47 (1956)

    CAS  Article  ADS  Google Scholar 

  8. Sørensen, G. O. & Pedersen, T. Symmetry and microwave spectrum of nitromethane. Stud. Phys. Theor. Chem. 23, 219–236 (1983)

    Google Scholar 

  9. Dawadi, M. B. et al. High-resolution Fourier transform infrared synchrotron spectroscopy of the NO2 in-plane rock band of nitromethane. J. Mol. Spectrosc. 315, 10–15 (2015)

    CAS  Article  ADS  Google Scholar 

  10. Albert, S. et al. Synchrotron-based highest resolution Fourier transform infrared spectroscopy of naphthalene (C10H8) and indole (C8H7N) and its application to astrophysical problems. Faraday Discuss. 150, 71–99 (2011)

    CAS  PubMed  Article  ADS  Google Scholar 

  11. Pirali, O. et al. Rotationally resolved infrared spectroscopy of adamantane. J. Chem. Phys. 136, 024310 (2012)

    CAS  PubMed  Article  ADS  Google Scholar 

  12. Pirali, O. & Boudon, V. Synchrotron-based Fourier transform spectra of the v23 and v24 IR bands of hexamethylenetetramine C6N4H12 . J. Mol. Spectrosc. 315, 37–40 (2015)

    CAS  Article  ADS  Google Scholar 

  13. Udem, T. et al. Absolute optical frequency measurement of the cesium D1 line with a mode-locked laser. Phys. Rev. Lett. 82, 3568–3571 (1999)

    CAS  Article  ADS  Google Scholar 

  14. Diddams, S. A. et al. Direct link between microwave and optical frequencies with a 300 THz femtosecond laser comb. Phys. Rev. Lett. 84, 5102–5105 (2000)

    CAS  PubMed  Article  ADS  Google Scholar 

  15. Adler, F. et al. Phase-stabilized, 1.5 W frequency comb at 2.8–4.8 μm. Opt. Lett. 34, 1330–1332 (2009)

    PubMed  Article  ADS  Google Scholar 

  16. Brown, G. G. et al. A broadband Fourier transform microwave spectrometer based on chirped pulse excitation. Rev. Sci. Instrum. 79, 053103 (2008)

    PubMed  Article  ADS  CAS  Google Scholar 

  17. Park, G. B. et al. Design and evaluation of a pulsed-jet chirped-pulse millimeter-wave spectrometer for the 70–102 GHz region. J. Chem. Phys. 135, 024202 (2011)

    PubMed  Article  ADS  CAS  Google Scholar 

  18. Patterson, D. & Doyle, J. M. Cooling molecules in a cell for FTMW spectroscopy. Mol. Phys. 110, 1757–1766 (2012)

    CAS  Article  ADS  Google Scholar 

  19. Piskorski, J. et al. Cooling, spectroscopy and non-sticking of trans-stilbene and Nile Red. ChemPhysChem 15, 3800–3804 (2014)

    CAS  PubMed  Article  Google Scholar 

  20. Cavagnat, D. & Lespade, L. Internal dynamics contributions to the CH stretching overtone spectra of gaseous nitromethane NO2CH3 . J. Chem. Phys. 106, 7946–7957 (1997)

    CAS  Article  ADS  Google Scholar 

  21. Davis, S. et al. Jet-cooled molecular radicals in slit supersonic discharges: sub-Doppler infrared studies of methyl radical. J. Chem. Phys. 107, 5661–5675 (1997)

    CAS  Article  ADS  Google Scholar 

  22. Brumfield, B. E., Stewart, J. T. & McCall, B. J. Extending the limits of rotationally resolved absorption spectroscopy: pyrene. J. Phys. Chem. Lett. 3, 1985–1988 (2012)

    CAS  Article  Google Scholar 

  23. Rohart, F. Microwave spectrum of nitromethane internal rotation Hamiltonian in the low barrier case. J. Mol. Spectrosc. 57, 301–311 (1975)

    CAS  Article  ADS  Google Scholar 

  24. Sørensen, G. O. et al. Microwave spectra of nitromethane and D3-nitromethane. J. Mol. Struct. 97, 77–82 (1983)

    Article  ADS  Google Scholar 

  25. Pimentel, G. C. & McClellan, A. L. The infrared spectra of naphthalene crystals, vapor, and solutions. J. Chem. Phys. 20, 270–277 (1952)

    CAS  Article  ADS  Google Scholar 

  26. Hewett, K. B. et al. High resolution infrared spectroscopy of pyrazine and naphthalene in a molecular beam. J. Chem. Phys. 100, 4077–4086 (1994)

    CAS  Article  ADS  Google Scholar 

  27. Pirali, O. et al. The far infrared spectrum of naphthalene characterized by high resolution synchrotron FTIR spectroscopy and anharmonic DFT calculations. Phys. Chem. Chem. Phys. 15, 10141–10150 (2013)

    CAS  PubMed  Article  Google Scholar 

  28. Muñoz Caro, G. M. et al. UV-photoprocessing of interstellar ice analogs: detection of hexamethylenetetramine-based species. Astron. Astrophys. 413, 209–216 (2004)

    Article  ADS  CAS  Google Scholar 

  29. Fleisher, A. J. et al. Mid-infrared time-resolved frequency comb spectroscopy of transient free radicals. J. Phys. Chem. Lett. 5, 2241–2246 (2014)

    CAS  PubMed  Article  Google Scholar 

  30. Thorpe, M. J. & Ye, J. Cavity-enhanced direct frequency comb spectroscopy. Appl. Phys. B 91, 397–414 (2008)

    CAS  Article  ADS  Google Scholar 

  31. Brubach, J. et al. Performance of the AILES THz-infrared beamline at SOLEIL for high resolution spectroscopy. AIP Conf. Proc. 1214, 81–84 (2010)

    Article  ADS  Google Scholar 

  32. Maslowski, P. et al. Surpassing the path-limited resolution of Fourier-transform spectrometry with frequency combs. Phys. Rev. A 93, 021802(R) (2016)

  33. Cox, A. P. & Waring, S. Microwave spectrum and structure of nitromethane. J. Chem. Soc. Faraday Trans. 2 68, 1060–1071 (1972)

    CAS  Article  Google Scholar 

  34. Jones, W. J. & Sheppard, N. The gas-phase infrared spectra of nitromethane and methyl boron difluoride; fine structure caused by internal rotation. Proc. R. Soc. Lond. A 304, 135–155 (1968)

    Article  ADS  Google Scholar 

  35. McKean, D. C. & Watt, R. A. Vibrational spectra of nitromethanes and the effects of internal rotation. J. Mol. Spectrosc. 61, 184–202 (1976)

    CAS  Article  ADS  Google Scholar 

  36. Hill, J. R. et al. Infrared, Raman, and coherent anti-Stokes Raman spectroscopy of the hydrogen/deuterium isotopomers of nitromethane. J. Phys. Chem. 95, 3037–3044 (1991)

    CAS  Article  Google Scholar 

  37. Gorse, D. et al. Theoretical and spectroscopic study of asymmetric methyl rotor dynamics in gaseous partially deuterated nitromethanes. J. Phys. Chem. 97, 4262–4269 (1993)

    CAS  Article  Google Scholar 

  38. Hazra, A., Ghosh, P. & Kshirsagar, R. Fourier transform infrared spectrum and rotational structure of the A-type 917.5 cm−1 band of nitromethane. J. Mol. Spectrosc. 164, 20–26 (1994)

    CAS  Article  ADS  Google Scholar 

  39. Hazra, A. & Ghosh, P. Assignment of the m = 0 transitions in the ν4 band of nitromethane by the symmetric top approximation method. J. Mol. Spectrosc. 173, 300–302 (1995)

    CAS  Article  ADS  Google Scholar 

  40. Pal, C. et al. High resolution Fourier transform infrared spectrum and vibration-rotation analysis of the B-type 1584 cm−1 band of nitromethane. J. Mol. Struct. 407, 165–170 (1997)

    CAS  Article  ADS  Google Scholar 

  41. Halonen, M. et al. Molecular beam infrared spectrum of nitromethane in the region of the first C-H stretching overtone. J. Phys. Chem. A 102, 9124–9128 (1998)

    CAS  Article  Google Scholar 

  42. Bunker, P. R. & Jensen, P. Molecular Symmetry and Spectroscopy 2nd edn (NRC Research Press, Ottawa, 1998)

  43. Watson, J. K. G. Vibrational Spectra and Structure Vol. 6, Ch. 1 (ed. Durig, J. ) (Elsevier, 1977)

  44. Townes, C. H. & Schawlow, A. L. Microwave Spectroscopy (Dover, 1975)

  45. Bemish, R. J. et al. Infrared spectroscopy and ab initio potential energy surface for Ne-C2H2 and Ne-C2HD complexes. J. Chem. Phys. 109, 8968–8978 (1998)

    CAS  Article  ADS  Google Scholar 

  46. Baer, T. & Hase, W. L. Unimolecular Reaction Dynamics (Oxford Univ. Press, 1996)

  47. Bistričić, L., Baranović, G. & Mlinarić-Majerski, K. A vibrational assignment of adamantane and some of its isotopomers. Empirical versus scaled semiempirical force field. Spectrochim. Acta A 51, 1643–1664 (1995)

    Article  ADS  Google Scholar 

  48. Jensen, J. O. Vibrational frequencies and structural determination of adamantane. Spectrochim. Acta A 60, 1895–1905 (2004)

    Article  ADS  CAS  Google Scholar 

  49. Sellers, H., Pulay, P. & Boggs, J. E. Theoretical prediction of vibrational spectra. 2. Force field, spectroscopically refined geometry, and reassignment of the vibrational spectrum of naphthalene. J. Am. Chem. Soc. 107, 6487–6494 (1985)

    CAS  Article  Google Scholar 

  50. Mitra, S. S. & Bernstein, H. J. Vibrational spectra of naphthalene-d0, -α-d4, and -d8 molecules. Can. J. Chem. 37, 553–562 (1959)

    CAS  Article  Google Scholar 

  51. Ramachandran, G. & Manogaran, S. Vibrational spectra of adamantanes X10H16 and diamantanes X14H20 (X = C, Si, Ge, Sn): a theoretical study. J. Mol. Struct. THEOCHEM 766, 125–135 (2006)

    CAS  Article  Google Scholar 

  52. Jenkins, T. & Lewis, J. A Raman study of adamantane (C10H16), diamantane (C14H20) and triamantane (C18H24) between 10 K and room temperatures. Spectrochim. Acta A 36, 259–264 (1980)

    Article  ADS  Google Scholar 

  53. Hudson, B. S. et al. Infrared, Raman, and inelastic neutron scattering spectra of dodecahedrane: an I h molecule in T h site symmetry. J. Phys. Chem. A 109, 3418–3424 (2005)

    CAS  PubMed  Article  Google Scholar 

  54. Karpushenkava, L. S., Kabo, G. J. & Bazyleva, A. B. Structure, frequencies of normal vibrations, thermodynamic properties, and strain energies of the cage hydrocarbons CnHn in the ideal-gas state. J. Mol. Struct. THEOCHEM 913, 43–49 (2009)

    CAS  Article  Google Scholar 

  55. Szczepanski, J. et al. Electronic and vibrational spectra of matrix isolated anthracene radical cations: experimental and theoretical aspects. J. Chem. Phys. 98, 4494–4511 (1993)

    CAS  Article  ADS  Google Scholar 

  56. Bakke, A. et al. Condensed aromatics. Part II. The five-parameter approximation of the in-plane force field of molecular vibrations. Z. Naturforsch. C 34a, 579–584 (1979)

    CAS  Article  ADS  Google Scholar 

  57. Vala, M. et al. Electronic and vibrational spectra of matrix-isolated pyrene radical cations: theoretical and experimental aspects. J. Phys. Chem. 98, 9187–9196 (1994)

    CAS  Article  Google Scholar 

  58. Shinohara, H., Yamakita, Y. & Ohno, K. Raman spectra of polycyclic aromatic hydrocarbons. Comparison of calculated Raman intensity distributions with observed spectra for naphthalene, anthracene, pyrene, and perylene. J. Mol. Struct. 442, 221–234 (1998)

    CAS  Article  ADS  Google Scholar 

  59. Pechukas, P. Comment on “Densities of vibrational states of given symmetry species”. J. Phys. Chem. 88, 828 (1984)

    CAS  Article  Google Scholar 

  60. Nesbitt, D. J. & Field, R. W. Vibrational energy flow in highly excited molecules: role of intramolecular vibrational redistribution. J. Phys. Chem. 100, 12735–12756 (1996)

    CAS  Article  Google Scholar 

  61. Buckingham, G. T., Chang, C.-H. & Nesbitt, D. J. High-resolution rovibrational spectroscopy of jet-cooled phenyl radical: the ν 19 out-of-phase symmetric CH stretch. J. Phys. Chem. A 117, 10047–10057 (2013)

    CAS  PubMed  Article  Google Scholar 

Download references

Acknowledgements

We acknowledge funding from DARPA SCOUT, AFOSR, NIST and NSF-JILA PFC for this research. J.M.D. and D.P. acknowledge funding from the NSF and HQOC. B.S. is supported through an NRC Postdoctoral Fellowship. O.H.H. is partially supported through a Humboldt Fellowship. P.B.C. is supported by the NSF GRFP (award no. DGE1144083). We thank J. Baraban for input and discussion. We thank D. Perry for providing us with G. O. Sørensen’s original nitromethane ground state data.

Author information

Authors and Affiliations

Authors

Contributions

P.B.C., D.P., J.M.D. and J.Y. originally designed this experiment. B.S., P.B.C. and J.Y. discussed and implemented the experimental technique, and B.S. and P.B.C. analysed all data. B.S., P.B.C., B.J.B. and O.H.H. operated laboratory equipment. All authors wrote the paper and contributed to technical discussions regarding this work.

Corresponding authors

Correspondence to Ben Spaun or Jun Ye.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Reduced term values of the rotational sub-levels of ν3 + ν6 (m = 0).

These are plotted against the total angular momentum, J (scaled as J(J + 1)). The reduced energies are equal to the absolute energy E, offset by 2,950 cm−1, minus J(J + 1) times the average of the B and C rotational constants. The solid lines connect sets of levels with respect to Ka (the projection of J onto the molecular inertial a axis) and their parity (e/f) symmetry label. For clarity, e and f states are shown in triangles and circles, respectively. States of different Ka values are shown in different colours. Inset, magnified view of the boxed area of the main plot, showing pairs of perturbed eigenstates, split symmetrically about the zeroth-order bright state position, are indicated in bold markers (see Methods for additional details).

Extended Data Figure 2 Evidence of cluster-free cooling.

The plot compares our measured buffer gas cooled C2H2 spectrum (bottom trace) with that of the Ne–C2H2 complex (upper trace; reprinted with permission from figure 1 of ref. 45, copyright 1998, AIP Publishing LLC). Three acetylene monomer transitions in the buffer gas cooled spectrum, including two hot band transitions and a 13C feature as described in the text, have been labelled. The buffer gas cooled spectrum has been rebinned with a bin size of 5 frequency elements (~40 MHz total).

Extended Data Figure 3 The vibrational density of states for several large hydrocarbons.

In increasing order, the total density of states (that is, not symmetry selected) versus vibrational energy is shown for adamantane (C10H16), naphthalene (C10H8), dodecahedrane (C20H20), diamantane (C14H20), anthracene (C14H10), and pyrene (C16H10). These curves were calculated using a direct state count algorithm and a combination of previously observed and calculated vibrational frequencies (see Methods for details). The horizontal line at 100 states per cm−1 marks the empirical threshold symmetry selected state density for IVR60,61. The vertical line at 3,000 cm−1 indicates the approximate energy for CH stretch fundamental vibrations.

Extended Data Table 1 Rotational Hamiltonian fit results
Extended Data Table 2 Line list for the 2,953 cm−1 band of nitromethane
Extended Data Table 3 Continued from Extended Data Table 2
Extended Data Table 4 Naphthalene ν29 band line list

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Spaun, B., Changala, P., Patterson, D. et al. Continuous probing of cold complex molecules with infrared frequency comb spectroscopy. Nature 533, 517–520 (2016). https://doi.org/10.1038/nature17440

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nature17440

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing