An official website of the United States government
Context.Accurate42Ti(p,γ)43V reaction rates are crucial for understanding the nucleosynthesis path of the rapid capture process (rpprocess) that occurs in X-ray bursts. Aims.We aim to improve the thermonuclear rates of42Ti(p,γ)43V based on more complete resonance information and a more accurate direct component, together with the recently released nuclear masses data. We also explore the impact of the newly obtained rates on therpprocess. Methods.We reevaluated the reaction rate of42Ti(p,γ)43V by the sum of the isolated resonance contribution instead of the Hauser-Feshbach statistical model. We used a Monte Carlo method to derive the associated uncertainties of new rates. The nucleosynthesis simulations were performed via the NuGrid post-processing code ppn. Results.The new rates differ from previous estimations due to the use of a series of updated resonance parameters and a direct S factor. Compared with the previous results from the Hauser-Feshbach statistical model, which assumes compound nucleus43V with a sufficiently high-level density in the energy region of astrophysical interest, large differences exist over the entire temperature region ofrp-process interest, up to two orders of magnitude. We consistently calculated the photodisintegration rate using our new nuclear masses via the detailed balance principle, and found the discrepancies among the different reverse rates are much larger than those for the forward rate, up to ten orders of magnitude at the temperature of 108K. Using a trajectory with a peak temperature of 1.95×109K, we performed therp-process nucleosynthesis simulations to investigate the impact of the new rates. Our calculations show that the adoption of the new forward and reverse rates result in abundance variations for Sc and Ca of 128% and 49%, respectively, compared to the variations for the statistical model rates. On the other hand, the overall abundance pattern is not significantly affected. The results of using new rates also confirm that therp-process path does not bypass the isotope43V. Conclusions.Our study found that the Hauser-Feshbach statistical model is inappropriate to the reaction rate evaluation for42Ti(p,γ)43V. The adoption of the new rates confirms that the reaction path of42Ti(p,γ)43V(p,γ)44Cr(β+)44V is a key branch of therpprocess in X-ray bursts.
more »
« less
This content will become publicly available on January 1, 2026
Continuous centrifugation and filtration for assessing the catalytic significance of metal nanoparticles forming in situ during the palladium-catalyzed arylation of N -methylindole
Continuous centrifugation of the reaction mixture can impact the trajectory of a palladium-catalyzed C–H arylation reaction in which catalytically relevant nanoparticles are formingin situfrom a molecular precatalyst.
more »
« less
- PAR ID:
- 10643115
- Publisher / Repository:
- Royal Society of Chemistry
- Date Published:
- Journal Name:
- Catalysis Science & Technology
- ISSN:
- 2044-4753
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
A facile metal‐free [2,3]‐sigmatropic rearrangement reaction of allyl sulfides viaN‐sulfilimine intermediates has been developed. Treatment of allyl sulfides with imino‐λ3‐iodanes in the presence of a catalytic amount of elemental iodine allowed the reaction to proceed under mild conditions and gave the correspondingN‐allylsulfenamide compounds in moderate to good yields. SeveralN‐allylsulfenamide structures have been confirmed by single‐crystal X‐ray crystallography. The reaction initially involves the sulfonylimino group transfer reaction between imino‐λ3‐iodane and the sulfur atom, resulting in the formation ofN‐sulfilimine species, followed by [2,3]‐sigmatropic rearrangement to form theN‐allylsulfenamide.more » « less
-
Abstract The hitherto elusive monobridged Ge(μ‐H)GeH (X1A′) molecule was prepared in the gas phase by bimolecular reaction of atomic germanium with germane (GeH4). Electronic structure calculations revealed that this reaction commenced on the triplet surface with the formation of a van der Waals complex, followed by insertion of germanium into a germanium‐hydrogen bond over a submerged barrier to form the triplet digermanylidene intermediate (HGeGeH3); the latter underwent intersystem crossing from the triplet to the singlet surface. On the singlet surface, HGeGeH3predominantly isomerized through two successive hydrogen shifts prior to unimolecular decomposition to Ge(μ‐H)GeH isomer, which is in equilibrium with the vinylidene‐type (H2GeGe) and dibridged (Ge(μ‐H2)Ge) isomers. This reaction leads to the formation of cyclic dinuclear germanium molecules, which do not exist on the isovalent C2H2surface, thus deepening our understanding of the role of nonadiabatic reaction dynamics in preparing nonclassical, hydrogen‐bridged isomers carrying main group XIV elements.more » « less
-
Heterochromatin is a gene-repressive protein–nucleic acid ultrastructure that is initially nucleated by DNA sequences. However, following nucleation, heterochromatin can then propagate along the chromatin template in a sequence-independent manner in a reaction termed spreading. At the heart of this process are enzymes that deposit chemical information on chromatin, which attracts the factors that execute chromatin compaction and transcriptional or co/post-transcriptional gene silencing. Given that these enzymes deposit guiding chemical information on chromatin they are commonly termed ‘writers’. While the processes of nucleation and central actions of writers have been extensively studied and reviewed, less is understood about how the spreading process is regulated. We discuss how the chromatin substrate is prepared for heterochromatic spreading, and howtrans-acting factors beyond writer enzymes regulate it. We examine mechanisms by whichtrans-acting factors in Suv39, PRC2, SETDB1 and SIR writer systems regulate spreading of the respective heterochromatic marks across chromatin. While these systems are in some cases evolutionarily and mechanistically quite distant, common mechanisms emerge which thesetrans-acting factors exploit to tune the spreading reaction.more » « less
