indoor-experimental-assessment-efficiency-irradiance-spot-achromatic

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass (ADG) Fresnel Lens for Concentrating Photovoltaics

We present a method to characterize achromatic Fresnel lenses for photovoltaic applications. The achromatic doublet on glass (ADG) Fresnel lens is ...

Universidad Politécnica de Madrid

1) Protonation at all possible sites of adamantane (C(10)H(16)) was studied at the MP2/6-311++G(3df,2p)//MP2/6-311++G(d,p) level. This provided values of the changes in the thermodynamic state functions for these processes. Whenever direct comparison was possible, the agreement with experimental data was very good. 2) By the same means, the reaction paths linking the various species obtained in these reactions were analyzed. 3) Fourier transform ion cyclotron resonance (FT-ICR) spectroscopy was used to determine the rate constants for proton transfer from 16 protonated reference bases to adamantane in the gas phase. Also, the rate constants for the formation of ionic products in these reactions were determined. 4) The experimental reaction rates were successfully predicted and refined on the basis of a simple mechanistic model based on the reaction profiles indicated above. 5) Our results hint at the potential usefulness of this approach for mechanistic studies.

Ab initio and experimental thermodynamic and kinetic study of proton-assisted bond activation in gaseous hydrocarbons: deconvolution of reaction efficiencies in the case of adamantane.

Dimethyldisulfide (I) is the simplest model of the biologically relevant family of disubstituted disulfides. The experimental study of its gas-phase protonation has provided, we believe for the first time, a precise value of its gas-phase basicity. This value agrees within 1 kJ mol-1 with the results of G3 calculations. Also obtained for the first time was the reaction rate constant for the bimolecular reaction between I and its protonated form, IH+, to yield methanethiol and a dimethyldithiosulfonium ion. This constant is of the order of magnitude of the collision limit. A computational mechanistic study based on the energetic profile of the reaction, completed with Fukui's and Bader's treatments of the reactants and transition states fully rationalizes the regioselectivity of the reaction as well as the existence of a shallow, flat Gibbs energy surface for the reaction. The mechanistic relevance of the chalcogen-chalcogen interaction and the C--H...S bonds has been demonstrated.

Activation of the disulfide bond and chalcogen-chalcogen interactions: an experimental (FTICR) and computational study.

How can a carbon atom be covalently bound to five ligands? The case of Si2(CH3)7+.

The acidity-enhancing effect of BH(3) in gas-phase phosphineboranes compared to the corresponding free phosphines is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. Thus, the enhancement of the acidity of protic acids by Lewis acids usually observed in solution is also observed in the gas phase. For example, the gas-phase acidities (GA) of MePH(2) and MePH(2)BH(3) differ by about 118 kJ mol(-1) (see picture).The gas-phase acidity of a series of phosphines and their corresponding phosphineborane derivatives was measured by FT-ICR techniques. BH(3) attachment leads to a substantial increase of the intrinsic acidity of the system (from 80 to 110 kJ mol(-1)). This acidity-enhancing effect of BH(3) is enormous, between 13 and 18 orders of magnitude in terms of ionization constants. This indicates that the enhancement of the acidity of protic acids by Lewis acids usually observed in solution also occurs in the gas phase. High-level DFT calculations reveal that this acidity enhancement is essentially due to stronger stabilization of the anion with respect to the neutral species on BH(3) association, due to a stronger electron donor ability of P in the anion and better dispersion of the negative charge in the system when the BH(3) group is present. Our study also shows that deprotonation of ClCH(2)PH(2) and ClCH(2)PH(2)BH(3) is followed by chloride departure. For the latter compound deprotonation at the BH(3) group is found to be more favorable than PH(2) deprotonation, and the subsequent loss of Cl(-) is kinetically favored with respect to loss of Cl(-) in a typical S(N)2 process. Hence, ClCH(2)PH(2)BH(3) is the only phosphineborane adduct included in this study which behaves as a boron acid rather than as a phosphorus acid.

The ever-surprising chemistry of boron: enhanced acidity of phosphine.boranes.

Hydrogen-bonding interactions involving 2-(trifluoromethyl)-1,1,1,3,3,3-hexafluoropropane (1H) and 1(-) have been quantitatively studied by means of Fourier transform ion cyclotron resonance spectrometry. The existence of the species (1HCl)(-) and (1H1)(-) was demonstrated, and their thermodynamic stabilities were determined experimentally and computationally. In addition, some of their structural features were analyzed.

Hydrogen-bonding interactions of (CF3)3CH and (CF3)3C- in the gas phase. An experimental (FT-ICR) and computational study.

We show that the radical cations of adamantane (C(10)H(16)(*+), 1H(*+)) and perdeuteroadamantane (C(10)D(16)(*+), 1D(*+)) are stable species in the gas phase. The radical cation of adamantylideneadamantane (C(20)H(28)(*+), 2H(*+)) is also stable (as in solution). By using the natural (13)C abundances of the ions, we determine the rate constants for the reversible isergonic single-electron transfer (SET) processes involving the dyads 1H(*+)/1H, 1D(*+)/1D and 2H(*+)/2H. Rate constants for the reaction 1H(*+)+1D <==> 1H+1D(*+) are also determined and Marcus' cross-term equation is shown to hold in this case. The rate constants for the isergonic processes are extremely high, practically collision-controlled. Ab initio computations of the electronic coupling (H(DA)) and the reorganization energy (lambda) allow rationalization of the mechanism of the process and give insights into the possible role of intermediate complexes in the reaction mechanism.

Single-electron self-exchange between cage hydrocarbons and their radical cations in the gas phase.

We have carried out a study of the energetics, structural, and physical properties of o-, m-, and p-hydroxybenzophenone neutral molecules, C(13)H(10)O(2), and their corresponding anions. In particular, the standard enthalpies of formation in the gas phase at 298.15 K for all of these species were determined. A reliable experimental estimation of the enthalpy associated with intramolecular hydrogen bonding in chelated species was experimentally obtained. The gas-phase acidities (GA) of benzophenones, substituted phenols, and several aliphatic alcohols are compared with the corresponding aqueous acidities (pK(a)), covering a range of 278 kJ.mol(-1) in GA and 11.4 in pK(a). A computational study of the various species shed light on structural effects and further confirmed the self-consistency of the experimental results.

Neutral, ion gas-phase energetics and structural properties of hydroxybenzophenones.

This work employs Fourier transform ion cyclotron resonance (FT-ICR) and the Gaussian quantum chemistry composite methods W1 and G2 to experimentally and computationally analyze gas-phase basicities (GB) for a series of weak bases in the basicity region around and below water. The study aims to clarify the long-standing discrepancy between reported GB values for weak bases obtained via high-pressure mass spectrometry (HPMS) and ICR; the ICR scale is observed to be more than 2 times contracted compared to the HPMS scale. The computational results of this work support published HPMS data. This agreement improves with increasing sophistication of the computational method and is excellent at the W1 level. Several equilibria were also re-examined experimentally using FT-ICR. In the experiments with some polyfluorinated weak bases (hexafluoro-2-propanol and nonafluoro-2-methyl-2-propanol), it was found that two protonation processes compete in the gas phase: protonation on oxygen and protonation on fluorine. In these species, protonation on fluorine proceeds faster and is statistically favored over protonation on oxygen but leads to cations that are thermodynamically less stable than oxygen-protonated cations. The process may also lead to the irreversible loss of HF. The rearrangement of fluorine-protonated cations to oxygen-protonated cations is very slow and is further suppressed by the process of HF abstraction. These results at least partially explain the discrepancy between published HPMS data and earlier FT-ICR findings and call for the utmost care in using FT-ICR for gas-phase basicity measurements of heavily fluorinated compounds. The narrower dynamic range of ICR necessitates the measurement of several problematic bases and produces some differences between the ICR results in the present work and the published HPMS data; the wider dynamic range allows HPMS to overcome these difficulties in connecting the ladder.

Gas-phase basicities around and below water revisited.

The dissociative photoionization of tetramethyltin (Me₄Sn) and hexamethylditin (Me₆Sn₂) has been investigated by threshold photoelectron-photoion coincidence (TPEPICO). Ions are energy-selected, and their 0 K dissociation onsets are measured by monitoring the mass spectra as a function of ion internal energy. Me₄Sn(+) dissociates rapidly by methyl loss, with a 0 K onset of E₀ = 9.382 ± 0.020 eV. The hexamethylditin ion dissociates slowly on the time scale of the experiment (i.e., during the 40 μs flight time to the detector) so that dissociation rate constants are measured as a function of the ion energy. RRKM and the simplified statistical adiabatic channel model (SSACM) are used to extrapolate the measured rate constants for methyl and Me₃Sn(•) loss to their 0 K dissociation onsets, which were found to be 8.986 ± 0.050 and 9.153 ± 0.075 eV, respectively. Updated values for the heats of formation of the neutral Me₄Sn and Me₆Sn₂ are used to derive the following 298.15 K gas-phase standard heats of formation, in kJ·mol⁻¹: Δ(f)H(m)(o)(Me₃Sn(+),g) = 746.3 ± 2.9; Δ(f)H(m)(o)(Me₅Sn₂(+),g) = 705.1 ± 7.5; Δ(f)H(m)(o)(Me₃Sn(•),g) = 116.6 ± 9.7; Δ(f)H(m)(o)(Me₂Sn,g) = 123.0 ± 16.5; Δ(f)H(m)(o)(MeSn(+),g) = 877.8 ± 16.4. These energetic values also lead to the following 298.15 K bond dissociation enthalpies, in kJ·mol⁻¹: BDE(Me₃Sn-Me) = 284.1 ± 9.9; BDE(Me₃Sn-SnMe₃) = 252.6 ± 14.8.

Dissociation dynamics and thermochemistry of tin species, (CH3)4Sn and (CH3)6Sn2, by threshold photoelectron-photoion coincidence spectroscopy.

We have studied the energetics and structural properties of trans-cinnamic acid (CA), o-, m-, and p-coumaric acids (2-, 3-, and 4-hydroxycinnamic acids), caffeic acid (3,4-dihydroxycinnamic acid), ferulic acid (4-hydroxy-3-methoxycinnamic acid), iso-ferulic acid (3-hydroxy-4-methoxycinnamic acid), and sinapic acid (3,5-dimethoxy-4-hydroxycinnamic acid). The experimental values of Δ(f)H(m)°(g), determined (in kJ·mol(-1)) for CA (-229.8 ± 1.9), p-coumaric acid (-408.0 ± 4.4), caffeic acid (-580.0 ± 5.9), and ferulic acid (-566.4 ± 5.7), allowed us to derive Δ(f)H(m)°(g) of o-coumaric acid (-405.6 ± 4.4), m-coumaric acid (-406.4 ± 4.4), iso-ferulic acid (-565.2 ± 5.7), and sinapic acid (-698.8 ± 4.1). From these values and by use of isodesmic/homodesmotic reactions, we studied the energetic effects of π-donor substituents (-OH and -OCH(3)) in cinnamic acid derivatives and in the respective benzene analogues. Our results indicate that the interaction between -OCH(3) and/or -OH groups in hydroxycinnamic acids takes place without significant influence of the propenoic fragment.

Energetics and structural properties, in the gas phase, of trans-hydroxycinnamic acids.

Reaction of alkali metals (Li, Na, K) with mesityldichlorophosphane (MesPCl2, Mes = 2,4,6-Me3C6H2) in ethereal solvents leads to formation of the corresponding mesitylphosphanides MPHMes in good purity and yield. (31)P NMR spectroscopic studies in deuterated solvents strongly support a mechanism of the reaction that involves protonation/disproportionation steps in which the solvent is the only possible proton source. Li(thf)(tmeda)PHMes (1), [Na(tmeda)(μ-PHMes)]∞ (2), and [K(pmdeta)(μ-PHMes)]2 (3) (tmeda = N,N,N',N'-tetramethylethylenediamine, pmdeta = N,N,N',N″,N″-pentamethyldiethylenetriamine) were obtained; in the solid state, 2 forms zigzag chains while 3 is a dimeric compound.

Facile one-step synthesis of MPHMes from MesPCl2 (M = Li, Na, K; Mes = 2,4,6-Me3C6H2).

We have studied thermochemical, thermophysical and structural properties of bisphenols A, E, F, and AP. In particular, the standard enthalpies of sublimation and the standard enthalpies of formation in the gas phase at 298.15 K for all these species were experimentally determined. A computational study, through M05-2X density functional theory, of the various species shed light on structural effects and further confirmed, by means of the isodesmic reaction scheme, the excellent consistency of the experimental results. Our results reflect also the fact that energetic substituent effects are transferable from diphenylalkanes to bisphenols.

Energetic and structural study of bisphenols.

This paper presents a novel Fresnel lens capable of significantly reducing chromatic aberration in solar applications. The optical performance of this achromatic lens has been analyzed through ray-tracing simulations, showing a concentration factor three times higher than that attained by a classic silicone on glass (SOG) Fresnel lens while maintaining the same acceptance angle. This should avoid the need for a secondary optical element, reducing the cost associated with its manufacturing and assembly and increasing the module reliability. The achromatic lens is made of inexpensive plastic and elastomer which allows a highly scalable and cost-competitive manufacturing process similar to the one currently used for the fabrication of SOG Fresnel lenses.

Rebeca Herrero

Instituto de Energía Solar

Universidad Politécnica de Madrid

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass (ADG) Fresnel Lens for Concentrating Photovoltaics

Rebeca Herrero

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Instituto de Energía Solar

Universidad Politécnica de Madrid

Indoor Experimental Assessment of the Efficiency and Irradiance Spot of the Achromatic Doublet on Glass (ADG) Fresnel Lens for Concentrating Photovoltaics

Instituto de Energía Solar