An official website of the United States government
We demonstrate a single-molecule technique that is compatible with high-precision measurements and obtain the spectrum of three molecular ion species. While the current result yields a modest spectral resolution due to a broad light source, we expect the method to ultimately provide a resolution comparable to quantum logic methods with significantly less stringent requirements. Adaptations of this technique will prove useful in a wide range of precision spectroscopy arenas including the search for parity-violating effects in chiral molecules.
more »
« less
Single Molecule Infrared Spectroscopy in the Gas Phase
Spectroscopy is a key analytical tool that provides valuable insight into molecular structure and is widely used to identify chemical samples. Tagging spectroscopy is a form of action spectroscopy in which the absorption of a single photon by a molecular ion is detected via the loss of a weakly attached, inert “tag” particle (e.g. He, Ne, N2).1–3 The absorption spectrum is derived from the tag loss rate as a function of incident radiation frequency. To date, all spectroscopy of gas phase polyatomic molecules has been restricted to large molecular ensembles, complicating spectral interpretation by the presence of multiple chemical and isomeric species. Here we present a novel tagging spectroscopic scheme to analyze the purest possible sample: a single gas phase molecule. We demonstrate this technique with the measurement of the infrared spectrum of a single tropylium (C7H7+ ) molecular ion; to our knowledge the first recorded spectrum of a single gas phase polyatomic molecule. Our method’s high sensitivity revealed spectral features previously unobserved using traditional tagging methods.4 Our approach in principle enables analysis of multi-component mixtures by identifying constituent molecules one at a time. Single molecule sensitivity extends action spectroscopy to rare samples, such as those of extraterrestrial origin,5,6 or to reactive reaction intermediates formed at number densities too low for traditional action methods.
more »
« less
- Award ID(s):
- 1912105
- PAR ID:
- 10429222
- Date Published:
- Journal Name:
- Nature
- ISSN:
- 0028-0836
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Fluorescence-encoded infrared (FEIR) spectroscopy is a vibrational spectroscopy technique that has recently demonstrated the capability of single-molecule sensitivity in solution without near-field enhancement. This work explores the practical experimental factors that are required for successful FEIR measurements in both the single-molecule and bulk regimes. We investigate the role of resonance conditions by performing measurements on a series of coumarin fluorophores of varying electronic transition frequencies. To analyze variations in signal strength and signal to background between molecules, we introduce an FEIR brightness metric that normalizes out measurement-specific parameters. We find that the effect of the resonance condition on FEIR brightness can be reasonably well described by the electronic absorption spectrum. We discuss strategies for optimizing detection quality and sensitivity in bulk and single-molecule experiments.more » « less
-
The absolute configuration of a molecule can be established by analysis of molecular rotational spectra of the analyte complexed with a small chiral molecule of known configuration. This approach of converting the analyte enantiomers, with identical rotational spectra, into diastereomers that can be distinguished spectroscopically is analogous to chiral derivatization in nuclear magnetic resonance (NMR) spectroscopy. For the rotational chiral tag method, the derivatization uses non-covalent interactions to install the new chiral center and avoids complications due to possible racemization of the analyte when covalent chemistry is used. The practical success of this method rests on the ability to attribute assigned rotational spectra to specific geometries of the diastereomeric homochiral and heterochiral tag complexes formed in the pulsed jet expansion that is used to introduce samples into the microwave spectrometer. The assignment of a molecular structure to an experimental rotational spectrum uses quantum chemistry equilibrium geometries to provide theoretical estimates of the spectrum parameters that characterize the rotational spectrum. This work reports the results of a high-sensitivity rotational spectroscopy study of the complexes formed between (3)-butyn-2-ol and verbenone. The rotational spectra of four homochiral and four heterochiral complexes are assigned. In addition, the 14 distinct, singly-substituted 13C isotopomer spectra of five of these species are assigned in natural abundance. Analysis of these spectra provides direct structural characterization of the complexes through determination of the carbon atom position coordinates. This data set is used to benchmark quantum chemistry calculations of candidate equilibrium geometries of the chiral tag complexes. The quantum chemistry calculations are limited to methods commonly used in the field of rotational spectroscopy. It is shown that the accuracy of the structures from quantum chemistry provides a high-confidence assignment of cluster geometries to the observed spectra. As a result, a high-confidence determination of the analyte (verbenone) absolute configuration is achieved.more » « less
-
Climate change resulting from releasing greenhouse gases into the atmosphere continues to affect the Earth’s ecosystem. This pressing issue is driving the development of novel technologies to sense and measure harmful gas emissions. In parallel, the evolution of wireless communication networks requires the wider deployment of mobile telecommunication infrastructure. The terahertz (THz) spectrum is currently under-utilized but is expected to feature in 6G. The use of this spectrum is explored simultaneously for ultra-broadband communication and atmospheric sensing. For atmospheric sensing, the absorption of THz signals by gas molecules is used to estimate atmospheric gas composition. Molecular absorption loss profiles for each gas isotopologue are taken from the HITRAN database and compared with data from transceivers in sensing mode. Preliminary results are presented, showing the effects of signal path loss and power spectral density. A 6G network architecture is proposed to indicate how 6G infrastructure can perform climate change sensing, in addition to its primary purpose of wireless communication.more » « less
-
This New Views article will highlight some recent advances in high sensitivity gas detection using direct infrared absorption frequency comb laser spectroscopy, with a focus on frequency comb use in chemical reaction kinetics and our own contribution to this field. Our recently implemented detection technique uses a combination of a 12.9 GHz free spectral range virtually imaged phased array and diffraction grating to spatially disperse the mid-infrared frequency comb onto a camera. Individual frequencies or ‘comb teeth’ of a 250 MHz repetition-rate frequency comb are able to be resolved. High molecular sensitivity is achieved by increasing the interaction path length using a Herriott multipass cell. High spectral resolution, broadband spectral coverage, and high molecular sensitivity are all achieved on an adjustable 1–50 µs timescale, making this frequency comb apparatus ideal for measuring chemical reaction kinetics where multiple absorbing species can be monitored simultaneously. This New Views article will also discuss some of the challenges and decisions that chemists might face in implementing this advanced physics technology in their own laboratory. Spatially dispersed 250 MHz mid-infrared frequency comb laser, with absorption of some frequencies by a dilute sample of methane. KEYWORDS: Frequency combs, chemical kinetics, trace gas detectionmore » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41586-023-06351-7
