An official website of the United States government
Conformer-Specific Spectroscopy and IR-Induced Isomerization of a Model γ-Peptide: Ac-γ 4 -Phe-NHMe
- Award ID(s):
- 1764148
- PAR ID:
- 10346349
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry A
- Volume:
- 126
- Issue:
- 11
- ISSN:
- 1089-5639
- Page Range / eLocation ID:
- 1837 to 1847
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
Agostic interactions were observed in the bound mesityl group in a series of iron compounds bearing a bis(NHC) pincer CCC ligand. The L-type ligand on [(CCC)Fe II Mes(L)] complexes influences the strength of the agostic interaction and is manifested in the upfield shift of the 1 H NMR resonance for the mesityl methyl resonances. The nature of the interaction was further investigated by density functional theory calculations, allowing rationalization of some unexpected trends and proving to be a powerful predictive tool.more » « less
-
Jentschel, M (Ed.)The nuclear structure of the98Zr nucleus was studied through theβ−decay of98Yg.s.at the TRIUMF-ISAC facility. The use of the 8π γ-ray spectrometer with its ancillary detectors SCEPTAR and PACES enabled γ-γ and γ-e−coincidence measurements as well as γ-γ angular correlations. The level spin assignments and transition mixing ratios obtained in this study were in good agreement with previous results. Furthermore, 12 previously unknown states in the low-energy region of98Zr were identified, including the 0+5and 0+6levels at 2418 and 2749 keV, respectively. The 2+and I=1 natures for multiple newly observed and previously known (but not firmly assigned) states have been established. Additionally, the previously assumed pureE2 character of the 2+2→ 2+1367.8-keV transition was confirmed.more » « less
-
Abstract We consider the combined effects that overshooting and the12C(α,γ)16O reaction rate have on variable white dwarf (WD) stellar models. We find that carbon–oxygen (CO) WD models continue to yield pulsation signatures of the current experimental12C(α,γ)16O reaction rate probability distribution function when overshooting is included in the evolution. These signatures hold because the resonating mantle region, encompassing ≃0.2M⊙in a typical ≃0.6M⊙WD model, still undergoes radiative helium burning during the evolution to a WD. Our specific models show two potential low-order adiabatic g-modes,g2andg6, that signalize the12C(α,γ)16O reaction rate probability distribution function. Both g-mode signatures induce average relative period shifts of ΔP/P= 0.44% and ΔP/P= 1.33% forg2andg6, respectively. We find thatg6is a trapped mode, and theg2period signature is inversely proportional to the12C(α,γ)16O reaction rate. Theg6period signature generally separates the slower and faster reaction rates, and has a maximum relative period shift of ΔP/P= 3.45%. We conclude that low-order g-mode periods from CO WDs may still serve as viable probes for the12C(α,γ)16O reaction rate probability distribution function when overshooting is included in the evolution.more » « less
-
Context.An accurate28P(p,γ)29S reaction rate is crucial to defining the nucleosynthesis products of explosive hydrogen burning in ONe novae. Using the recently released nuclear mass of29S, together with a shell model and a direct capture calculation, we reanalyzed the28P(p,γ)29S thermonuclear reaction rate and its astrophysical implication. Aims.We focus on improving the astrophysical rate for28P(p,γ)29S based on the newest nuclear mass data. Our goal is to explore the impact of the new rate and associated uncertainties on the nova nucleosynthesis. Methods.We evaluated this reaction rate via the sum of the isolated resonance contribution instead of the previously used Hauser-Feshbach statistical model. The corresponding rate uncertainty at different energies was derived using a Monte Carlo method. Nova nucleosynthesis is computed with the 1D hydrodynamic code SHIVA. Results.The contribution from the capture on the first excited state at 105.64 keV in28P is taken into account for the first time. We find that the capture rate on the first excited state in28P is up to more than 12 times larger than the ground-state capture rate in the temperature region of 2.5 × 107K to 4 × 108K, resulting in the total28P(p,γ)29S reaction rate being enhanced by a factor of up to 1.4 at ~1 × 109K. In addition, the rate uncertainty has been quantified for the first time. It is found that the new rate is smaller than the previous statistical model rates, but it still agrees with them within uncertainties for nova temperatures. The statistical model appears to be roughly valid for the rate estimation of this reaction in the nova nucleosynthesis scenario. Using the 1D hydrodynamic code SHIVA, we performed the nucleosynthesis calculations in a nova explosion to investigate the impact of the new rates of28P(p,γ)29S. Our calculations show that the nova abundance pattern is only marginally affected if we use our new rates with respect to the same simulations but statistical model rates. Finally, the isotopes whose abundance is most influenced by the present28P(p,γ)29S uncertainty are28Si,33,34S,35,37Cl, and36Ar, with relative abundance changes at the level of only 3% to 4%.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.jpca.2c00112
