Ergodicity breaking in rapidly rotating C60 fullerenes Liu, Lee R; Rosenberg, Dina; Changala, P Bryan ...
Science (American Association for the Advancement of Science),
08/2023, Letnik:
381, Številka:
6659
Journal Article
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Editor’s summaryErgodicity breaking, the inability of a system to thermalize, is of fundamental interest in statistical mechanics and physics and has been vigorously studied in many systems. Using ...high-sensitivity infrared spectroscopy, Liu et al. collected compelling experimental signatures of previously unobserved rotational ergodicity breaking in a buckminsterfullerene molecule (C60) that arose from rotation-vibration coupling and were distinctly different from what was found in all prior studies. Because of its symmetry, size, and rigidity, C60 can switch back and forth between ergodic and non-ergodic rotational regimes as it rotates faster and faster. The present work reports peculiar rotational dynamics in C60 and demonstrates how such a familiar but relatively unexplored molecule can be used to observe new phenomena. —Yury Suleymanov
We report high-resolution photoelectron spectra of the simplest carbanions, CH3 – and CD3 –. The vibrationally resolved spectra are dominated by a long progression in the umbrella mode (ν2) of •CH3 ...and •CD3, indicating a transition from a pyramidal C 3v anion to the planar D 3h methyl radical. Analysis of the spectra provides electron affinities of •CH3 (0.093(3) eV) and •CD3 (0.082(4) eV). These results enable improved determination of the corresponding gas-phase acidities: Δacid H 0K°(CH4) = 414.79(6) kcal/mol and Δacid H 0K°(CD4) = 417.58(8) kcal/mol. On the basis of the photoelectron anisotropy distribution, the electron is photodetached from an orbital with predominant p-character, consistent with the sp3-hybridized orbital picture of the pyramidal anion. The double-well potential energy surface along the umbrella inversion coordinate leads to a splitting of the vibrational energy levels of the umbrella mode. The inversion splittings of CH3 – and CD3 – are 21(5) and 6(4) cm–1, respectively, and the corresponding anion umbrella vibrational frequencies are 444(13) and 373(12) cm–1, respectively. Quantum mechanical calculations reported herein show good agreement with the experimental data and provide insight regarding the electronic potential energy surface of CH3 –.
The rotational spectra of the singly substituted carbon-13 isotopic species of six sulphur-terminated carbon chains have been detected between 5 and 40 GHz using a supersonic discharge jet source in ...combination with a cavity Fourier transform microwave spectrometer. These molecules are
, a closed-shell isomer of
, and five radicals:
,
,
,
and
. Experiments were carried out with precursors enriched in
C, either high purity
, a statistical sample of
C/
C acetylene, or
. From the
C hyperfine coupling constants, the unpaired electronic density along the chain can be quantified for the radical species, while precise experimental structures (
) can be derived for each chain except
by a least-squares fit to the rotational constants. The use of
is particularly revealing in that it provides important clues as to the major formation pathway for each chain in our discharge nozzle. Somewhat surprisingly,
C from this precursor appears to be substituted in one of three distinct ways: statistical, a single C site, or not at all. This propensity is molecule specific, implying that multiple formation pathways are operative.
Isoprene (2-methyl-1,3-butadiene) is highly abundant in the atmosphere, second only to methane in hydrocarbon emissions. In contrast to the most stable trans rotamer, structural characterization of ...gauche-isoprene has proven challenging: it is weakly polar, present at the level of only a few percent at room temperature, and structurally complex due to both torsional and methyl tunneling motions. gauche-Isoprene has been observed by two distinct but complementary experimental approaches: chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy coupled with cryogenic buffer gas cooling, and cavity-enhanced FTMW spectroscopy with a pulsed discharge source. Thermal enhancement of the gauche population (from 1.7% to 10.3%) was observed in the cryogenic buffer gas cell when the sample was preheated from 300 to 450 K, demonstrating that high-energy rotamers can be efficiently isolated under our experimental conditions. Rotational parameters for the inversion states (0+/0–) have been determined for the first time, aided by calculations at increasing levels of theoretical sophistication. From this combined analysis, the inversion splitting ΔE and the F bc Coriolis coupling constant between the two inversion states have been derived.
The high resolution far-infrared spectrum of trans-butadiene has been reinvestigated by Fourier-transform spectroscopy at two synchrotron radiation facilities, SOLEIL and the Canadian Light Source, ...at temperatures ranging from 50 to 340 K. Beyond the well-studied bands, two new fundamental bands lying below 1100 cm–1, ν10 and ν24, have been assigned using a combination of cross-correlation (ASAP software) and Loomis-Wood type (LWWa software) diagrams. While the ν24 analysis was rather straightforward, ν10 exhibits obvious signs of a strong perturbation, presumably owing to interaction with the dark ν9 + ν12 state. Effective rotational constants have been derived for both the v 10 = 1 and v 24 = 1 states. Since only one weak, infrared active fundamental band (ν23) of trans-butadiene remains to be observed at high resolution in the far-infrared, searches for the elusive gauche conformer can now be undertaken with considerably greater confidence in the dense ro-vibrational spectrum of the trans form.
Rotational spectroscopy is an invaluable tool to unambiguously determine the molecular structure of a species, and sometimes even to establish its very existence. This article illustrates how ...experimental and theoretical state‐of‐the‐art tools can be used in tandem to investigate the rotational structure of molecules, with particular emphasis on those that have long remained elusive. The examples of three emblematic species—gauche‐butadiene, disilicon carbide, and germanium dicarbide—highlight the close, mutually beneficial interaction between high‐level theoretical calculations and sensitive microwave measurements. Prospects to detect other elusive molecules of chemical and astronomical interest are discussed.
Hunting elusive species: Close coordination of theoretical calculations and rotational spectroscopy can be used efficiently to detect and structurally characterize several elusive species, as gauche‐butadiene, SiCSi, and GeC2, three emblematic species for which the experimental observation was only made possible by this close interaction (see picture).
Quantitative and mechanistically detailed kinetics of the reaction of hydroxyl radical (OH) with carbon monoxide (CO) have been a longstanding goal of contemporary chemical kinetics. This fundamental ...prototype reaction plays an important role in atmospheric and combustion chemistry, motivating studies for accurate determination of the reaction rate coefficient and its pressure and temperature dependence at thermal reaction conditions. This intricate dependence can be traced directly to details of the underlying dynamics (formation, isomerization, and dissociation) involving the reactive intermediates
- and
-HOCO, which can only be observed transiently. Using time-resolved frequency comb spectroscopy, comprehensive mechanistic elucidation of the kinetics of the isotopic analog deuteroxyl radical (OD) with CO has been realized. By monitoring the concentrations of reactants, intermediates, and products in real time, the branching and isomerization kinetics and absolute yields of all species in the OD + CO reaction are quantified as a function of pressure and collision partner.
To unambiguously identify new chemical species, and sometimes even to establish their very existence, rotationally resolved spectroscopy has proven to be an invaluable tool. In their Minireview on ...page 7243 ff., M. C. McCarthy and co‐workers, illustrate the power of closely coordinating experiment and theory to investigate the rotational pattern of several elusive molecules and subsequent isotopic studies to accurately determine their molecular structures. In this manner long standing controversies as to the most stable structural arrangement (e.g., planar or twisted; linear or cyclic) have been resolved.
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