Nine Ce ii lines have been identified and characterized within the spectral window observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey (between λ1.51 and 1.69 m). ...At solar metallicities, cerium is an element that is produced predominantly as a result of the slow capture of neutrons (the s-process) during asymptotic giant branch stellar evolution. The Ce ii lines were identified using a combination of a high-resolution ( ) Fourier Transform Spectrometer (FTS) spectrum of Boo and an APOGEE spectrum (R = 22,400) of a metal-poor, but s-process enriched, red giant (2M16011638-1201525). Laboratory oscillator strengths are not available for these lines. Astrophysical gf-values were derived using Boo as a standard star, with the absolute cerium abundance in Boo set by using optical Ce ii lines that have precise published laboratory gf-values. The near-infrared Ce ii lines identified here are also analyzed, as consistency checks, in a small number of bright red giants using archival FTS spectra, as well as a small sample of APOGEE red giants, including two members of the open cluster NGC 6819, two field stars, and seven metal-poor N- and Al-rich stars. The conclusion is that this set of Ce ii lines can be detected and analyzed in a large fraction of the APOGEE red giant sample and will be useful for probing chemical evolution of the s-process products in various populations of the Milky Way.
We present 5-40 mu m spectroscopy of 41 planetary nebulae (PNe) in the Magellanic Clouds, observed with the Infrared Spectrograph on board the Spitzer Space Telescope. The spectra show the presence ...of a combination of nebular emission lines and solid state features from dust, superimposed on the thermal IR continuum. By analyzing the 25 LMC and 16 SMC PNe in our sample we found that the IR spectra of 14 LMC and four SMC PNe are dominated by nebular emission lines, while the other spectra show solid state features. We observed that the solid state features are compatible with carbon-rich dust grains (SiC, polycyclic aromatic hydrocarbons PAHs, etc.) in all cases but three PNe, which show oxygen-rich dust features. The frequency of carbonaceous dust features is generally higher in LMC than in SMC PNe. The spectral analysis allowed the correlations of the dust characteristics with the gas composition and morphology, and the properties of the central stars. We found that (1) all PNe with carbonaceous dust features have C/O > 1, none of these being bipolar or otherwise highly asymmetric; (2) all PNe with oxygen-rich dust features have C/O < 1, with probable high-mass progenitors if derived from single-star evolution (these PNe are either bipolar or highly asymmetric); (3) the dust temperature tracks the nebular and stellar evolution; and (4) the dust production efficiency depends on metallicity, with low-metailicity environments not favoring dust production.
The KMnO
4
oxidation reaction of C
60
or C
70
fullerenes in benzene solution proceeds smoothly and almost quantitatively in presence of the crown ether 18-crown-6 as phase-transfer agent. The ...oxidation reaction was followed spectrophotometrically from the early stages to the completion. Essentially fullerenols or polyhydroxylated fullerenes were produced as confirmed also by FT-IR spectroscopy. The resulting degree of hydroxylation of both C
60
and C
70
was determined as C
60
(OH)
28
and C
70
(OH)
26
. As secondary structures, also epoxide and carboxylic groups were detected.
A study on poly(indene) Cataldo, Franco; Barzaga, Ransel; García-Hernández, D. Aníbal ...
Journal of macromolecular science. Part A, Pure and applied chemistry,
07/2024, Letnik:
61, Številka:
7
Journal Article
Recenzirano
Indene was polymerized to polyindene (PI) through a cationic mechanism using TiCl
4
*2THF complex as initiator. The cationic mechanism was investigated through electronic absorption spectroscopy and ...either the indanyl cation as well as the polyindenyl cation absorption bands were distinguished and assigned. The PI structure was investigated through the indane model compound and the indene reference compound electronic absorption spectra. Furthermore, the Raman spectrum of PI was recorded for the first time and the complete Raman and FT-IR absorption bands of PI are reported with the assignment of the main bands. The glass transition (T
g
) of cationic, radiation-induced and thermally initiated PI were measured through DSC and the corresponding molecular weight estimated. DSC and TGA-FTIR analysis were used to study the thermal decomposition of PI. It was assessed that PI is pyrolyzed back into indene monomer in almost theoretical yield with an activation enthalpy of E
#
= 164 kJ/mol while the decomposition enthalpy of PI was determined at 101.6 kJ/mol a value very close to the theoretical value of 108.9 kJ/mol. It was assessed that PI is a fully recyclable polymer which could be decomposed back to the monomer and re-polymerized at will.
A smooth, solventless and solid state debromination of C
70
Br
10
can be achieved in a CsI matrix with quantitative restoration of the pristine C
70
in quantitative yields. The debromination kinetics ...was studied with FT-IR spectroscopy and according to the pseudofirst order kinetics law, the rate constant was found in the range 3.6-5.2 × 10
−5
s
−1
. The compound C
70
Br
10
was studied with TGA and its thermal decomposition by DSC analysis. From the DSC data both the activation energy for the thermal decomposition of C
70
Br
10
was determined as well as its enthalpy of formation, which has led to some considerations on the relative weakness of C-Br bonds in brominated fullerenes compounds. The debromination mechanism is discussed in terms of unimolecular elimination reaction (E1) in a concerted mechanism which leads to the restoration of the pristine C
70
fullerene.
The bromofullerene C
60
Br
24
undergoes a complete and quantitative debromination to C
60
when it is mixed and ground in the solid state with cesium iodide (CsI). The kinetics of this unique solid ...state debromination reaction was studied with FT-IR spectroscopy on C
60
Br
24
embedded in CsI pellet. The debromination rate constant was measured k = 8.4 x 10
−4
s
−1
and found independent from the C
60
Br
24
concentration. Chemical thermodynamics calculations show that the C
60
Br
24
debromination in CsI matrix is characterized by a largely favorable free energy of reaction (ΔG
r
) and the reaction is exothermal. A debromination mechanism is discussed in terms of concerted elimination of the bromide anions and formation of carbocations on the fullerene cage in agreement with the E1 type elimination reaction mechanism. The carbocations sites are reduced to radicals and stabilized as trivinylmethyl radicals (the reduction occurs by the action of iodide ions of CsI which are oxidized to molecular iodine) and then a rearrangement of the double bonds leads back to C
60
quantitatively.
Thermochemical properties of C60Br24 Cataldo, Franco; Barzaga, Ransel; García-Hernández, D. Aníbal ...
Fullerenes, nanotubes, and carbon nanostructures,
06/2023, Letnik:
31, Številka:
6
Journal Article
Recenzirano
The thermal decomposition of C
60
Br
24
*2Br
2
has been studied by Differential Scanning Calorimetry (DSC) at different heating rates. Depending from the heating rate, the thermal decomposition peak ...occurred between 163 °C and 201 °C with an activation energy E
#
= 108.6 kJ/mol. The decomposition products are C
60
(assessed by FT-IR) and molecular bromine. From the decomposition enthalpy measured by DSC, the enthalpy of formation ΔH
f
°(C
60
Br
24(c)
) = 2114 ± 34 kJ/mol has been determined. By group increment or group additivity method ΔH
f
°(C
60
Br
24 (g)
) = 2184 kJ/mol has been calculated, in fair agreement with the experimental value. Furthermore, through the group increment method ΔG
f
°(C
60
Br
24 (g)
) = 3264 kJ/mol has been estimated. The enthalpy of the C-Br bond in the C
60
Br
24
molecule was found comprised between 108 and 120 kJ/mol.
Synthesis of a new C 60 cyanofullerene derivative Cataldo, Franco; Barzaga, Ransel; García-Hernández, D. Aníbal ...
Fullerenes, nanotubes, and carbon nanostructures,
07/2023, Letnik:
31, Številka:
7
Journal Article
The molar extinction coefficient ε and the integrated molar absorptivity ψ values of all the mid-infrared and far-infrared absorption bands of Li@C
60
+
PF
6
-
were determined in comparison to those ...of C
60
. The dependence from temperature of all the infrared absorption bands of Li@C
60
+
PF
6
-
was measured in the temperature range comprised from 523 K and 90 K and extrapolated to 0 K. Once again, the results were discussed in comparison to the C
60
analogous experimental results.
Both C
60
fullerene and indene were detected in certain astrophysical objects. It is then possible that these two molecules may react together in space forming adducts like indene-C
60
mono-adduct ...(ICMA) as well as the indene-C
60
bis-adducts (ICBA). In view of the potential detection of such adducts in space, the chemical thermodynamics of the reaction between C
60
and indene was analyzed using the thermochemical group increment approach. ICMA and ICBA were synthesized and their composition and stability was studied with thermogravimetric analysis and derivative thermogravimetry (TGA-DTG). ICBA and moreover ICMA resulted stable and strong adducts. In particular, the latter is stable up to 350 °C and this fact increases the chances to find it in space.
Furthermore, the retro Diels-Alder reaction was accurately studied on ICMA with differential scanning calorimetry (DSC) and an unusually high activation energy for the decomposition was determined and explained with the chemical thermodynamic data. The electronic absorption spectra of ICMA and ICBA were studied in n-hexane and the molar extinction coefficients of the main absorption bands have been determined. A possible way to detect such adducts is through electronic absorption spectroscopy, while the infrared spectroscopy of ICMA and ICBA is analyzed and discussed in the following second part of this work.
PDF
