An official website of the United States government
This paper presents an extensive parameter study of a non-intrusive and non-seeded laser diagnostic method for measuring one dimensional (1D) rotational temperature of molecular nitrogen (N2) at 165 - 450 K. Compared to previous efforts using molecular oxygen, here resonantly ionized and photoelectron induced fluorescence of molecular nitrogen for thermometry (N2RIPT) was demonstrated. The RIPT signal is generated by directly probing various rotational levels within the rovibrational absorption band of N2, corresponding to the 3-photon transition of N2(X1Σg+,v=0→b1Πu,v′=6) near 285 nm, without involving collisional effects of molecular oxygen and nitrogen. The photoionized N2produces strong first negative band of N2+(B2Σu+−X2Σg+) near 390 nm, 420 nm, and 425 nm. Boltzmann analyses of various discrete fluorescence emission lines yield rotational temperatures of molecular nitrogen. By empirically choosing multiple rotational levels within the absorption band, non-scanning thermometry can be accurately achieved for molecular nitrogen. It is demonstrated that the N2RIPT technique can measure 1D temperature profile up to ∼5 cm in length within a pure N2environment. Multiple wavelengths are thoroughly analyzed and listed that are accurate for RIPT for various temperature ranges.
more »
« less
Attosecond electronic dynamics of core-excited states of N2O probed by transient soft X-ray spectroscopy
Half-cycle oscillation is observed in transient absorption spectra of N2O at NKedge (400 eV) irradiated by intense IR pulses, which is attributed to tunneling ionization of core excited states by intensive TDSE-based simulation.
more »
« less
- Award ID(s):
- 1912507
- PAR ID:
- 10360809
- Date Published:
- Journal Name:
- The International Conference on Ultrafast Phenomena (UP) 2022
- Page Range / eLocation ID:
- W1A.3
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Simple synthetic routes to regioselectively deuterated tris[2‐(dimethylamino)ethyl]amine (Me6TREN) variants are described. Imine formation with formaldehyde‐d2from tris(2‐aminoethyl)amine (TREN) and subsequent reductions with NaBD4afforded N[CH2CH2N(CD3)2]3ord18‐Me6TREN in 79 % yield. A trisubstitution protocol from 2‐bromo‐N,N‐dimethylacetamide and ammonium carbonate and subsequent reduction of the N(CH2CONMe2)3intermediate by lithium aluminum deuteride has afforded N[CH2CD2N(CH3)2]3or (d6‐arm)‐Me6TREN in three steps and 52 % overall yield. A similar protocol from 2‐bromo‐N,N‐dimethyl‐d2‐acetamide, obtained in two steps fromd4‐acetic acid, with reduction of the N(CD2CONMe2)3intermediate by lithium aluminum hydride has afforded N[CD2CH2N(CH3)2]3or (d6‐cap)‐Me6TREN in four steps and 13 % overall yield from CD3COOD.more » « less
-
Context. Carbon monoxide (CO) is a poor tracer of H2in the diffuse interstellar medium (ISM), where most of the carbon is not incorporated into CO molecules, unlike the situation at higher extinctions. Aims. We present a novel, indirect method for constraining H2column densities (NH2) without employing CO observations. We show that previously recognized nonlinearities in the relation between the extinction,AV(H2), derived from dust emission and the H Icolumn density (NH I) are due to the presence of molecular gas. Methods. We employed archival (NH2) data, obtained from the UV spectra of stars, and calculatedAV(H2) toward these sight lines using 3D extinction maps. The following relation fits the data: logNH2= 1.38742 (logAV(H2))3− 0.05359 (logAV(H2))2+ 0.25722 logAV(H2) + 20.67191. This relation is useful for constrainingNH2in the diffuse ISM as it requires onlyNH Iand dust extinction data, which are both easily accessible. In 95% of the cases, the estimates produced by the fitted equation have deviations of less than a factor of 3.5. We constructed aNH2map of our Galaxy and compared it to the CO integrated intensity (WCO) distribution. Results. We find that the average ratio (XCO) betweenNH2andWCOis approximately equal to 2 × 1020cm−2(K km s−1)−1, consistent with previous estimates. However, we find that theXCOfactor varies by orders of magnitude on arcminute scales between the outer and the central portions of molecular clouds. For regions withNH2≳ 1020cm−2, we estimate that the average H2fractional abundance,fH2= 2NH2/(2NH2+NH I), is 0.25. Multiple (distinct) largely atomic clouds are likely found along high-extinction sightlines (AV≥ 1 mag), hence limitingfH2in these directions. Conclusions. More than 50% of the lines of sight withNH2≥ 1020cm−2are untraceable by CO with aJ= 1−0 sensitivity limitWCO= 1 K km s−1.more » « less
-
PREMISEBiological invasions increasingly threaten native biodiversity and ecosystem services. One notable example is the common reed,Phragmites australis, which aggressively invades North American salt marshes. Elevated atmospheric CO2and nitrogen pollution enhance its growth and facilitate invasion becauseP. australisresponds more strongly to these enrichments than do native species. We investigated how modifications to stomatal features contribute to strong photosynthetic responses to CO2and nitrogen enrichment inP. australisby evaluating stomatal shifts under experimental conditions and relating them to maximal stomatal conductance (gwmax) and photosynthetic rates. METHODSPlants were grownin situin open‐top chambers under ambient and elevated atmospheric CO2(eCO2) and porewater nitrogen (Nenr) in a Chesapeake Bay tidal marsh. We measured light‐saturated carbon assimilation rates (Asat) and stomatal characteristics, from which we calculatedgwmaxand determined whether CO2and Nenraltered the relationship betweengwmaxandAsat. RESULTSeCO2and Nenrenhanced bothgwmaxandAsat, but to differing degrees;gwmaxwas more strongly influenced by Nenrthrough increases in stomatal density whileAsatwas more strongly stimulated by eCO2. There was a positive relationship betweengwmaxandAsatthat was not modified by eCO2or Nenr, individually or in combination. CONCLUSIONSChanges in stomatal features co‐occur with previously described responses ofP. australisto eCO2and Nenr. Complementary responses of stomatal length and density to these global change factors may facilitate greater stomatal conductance and carbon gain, contributing to the invasiveness of the introduced lineage.more » « less
-
A<sc>bstract</sc> A search for long-lived heavy neutrinos (N) in the decays of B mesons produced in proton-proton collisions at$$ \sqrt{s} $$ = 13 TeV is presented. The data sample corresponds to an integrated luminosity of 41.6 fb−1collected in 2018 by the CMS experiment at the CERN LHC, using a dedicated data stream that enhances the number of recorded events containing B mesons. The search probes heavy neutrinos with masses in the range 1 <mN< 3 GeV and decay lengths in the range 10−2<cτN< 104mm, where τNis the N proper mean lifetime. Signal events are defined by the signature B →ℓBNX; N →ℓ±π∓, where the leptonsℓBandℓcan be either a muon or an electron, provided that at least one of them is a muon. The hadronic recoil system, X, is treated inclusively and is not reconstructed. No significant excess of events over the standard model background is observed in any of theℓ±π∓invariant mass distributions. Limits at 95% confidence level on the sum of the squares of the mixing amplitudes between heavy and light neutrinos, |VN|2, and oncτNare obtained in different mixing scenarios for both Majorana and Dirac-like N particles. The most stringent upper limit|VN|2< 2.0×10−5is obtained atmN= 1.95 GeV for the Majorana case where N mixes exclusively with muon neutrinos. The limits on|VN|2for masses 1 <mN< 1.7 GeV are the most stringent from a collider experiment to date.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1364/UP.2022.W1A.3
