China
Africa
Explore chapters and articles related to this topic
Chemical Rocket Propellants
Published in D.P. Mishra, Fundamentals of Rocket Propulsion, 2017
Several kinds of liquid oxidizers that can be used as propellant in rocket engines have been devised and developed. These oxidizer compounds mainly contain some atoms of oxygen, fluorine, chlorine, hydrogen, nitrogen, boron, and so on. Some examples of liquid oxidizers (see Table 6.6) are hydrogen peroxide, nitric acid, liquid oxygen, ozone, nitrogen peroxide, liquid fluorine, chlorine trifluoride, chlorine pentafluoride, nitrogen trifluoride, and oxygen difluoride. Some of these oxidizers are not being used nowadays. Some common liquid oxidizers that are being used in liquid-propellant rocket engines are discussed in the following.
List of Chemical Substances
Published in T.S.S. Dikshith, and Safety, 2016
Acetylene (100% purity) is odorless but commercial purity has a distinctive garlic-like odor. It is very soluble in alcohol and almost miscible with ethane. Acetylene is a flammable gas and kept under pressure in gas cylinders. Under certain conditions, acetylene can react with copper, silver, and mercury to form acetylides, compounds that can act as ignition sources. Brasses contain a form acetylides, compounds that can act as ignition sources. Brasses containing less than 65% copper in the alloy and certain nickel alloys are suitable for acetylene. Acetylene is not compatible with strong oxidizers such as chlorine, bromine pentafluoride, oxygen, oxygen difluoride, and nitrogen trifluoride, brass metal, calcium hypochlorite, heavy metals such as copper, silver, mercury, and their salts, bromine, chlorine, iodine, fluorine, sodium hydride, cesium hydride, ozone, perchloric acid, or potassium.
Electrochemistry
Published in Franco Battaglia, Thomas F. George, Understanding Molecules, 2018
Franco Battaglia, Thomas F. George
Determining the oxidation number (o.n.) of an element in a chemical species is easier if the following practical rules are applied: The sum of the oxidation numbers of all the elements in a species is equal to the number (positive or negative) of elementary charges of that species.The o.n. of an element in a neutral homonuclear molecule is equal to 0. For instance, in H2, O2, O3, and C60, the hydrogen, oxygen or carbon o.n. is equal to zero.The o.n. of the I group elements (alkaline metals) is equal to +1 in all their compounds (it is 0 in the elemental species); the o.n. of the II group elements (alkaline-earth metals) is equal to +2 in all their compounds (it is 0 in the elemental species).The o.n. of fluorine is always –1 (except, of course, in F2).The o.n. of hydrogen is always +1, except in metallic hydrides, in which hydrogen has o.n. equal to –1 (and, of course, except in H2). For instance, in LiH (lithium hydride), the lithium o.n. is +1, and the hydrogen o.n. is equal to –1; in H2O the hydrogen o.n. is +1, and consequently the oxygen o.n. is –2; and in H2O2 (hydrogen peroxide), the hydrogen o.n. is +1, and consequently the oxygen o.n. is equal to –1.The o.n. of oxygen is always –2, except where it is present in the form of a peroxide, i.e., with a −O−O− bond, and except where rules (c) or (d) apply. For instance, the oxygen o.n. is +2 in OF2 (oxygen difluoride), and +(1/2) in KO2 (potassium superoxide).
Potential energy surfaces of charge transfer states
Published in Molecular Physics, 2020
Balázs Kozma, Romain Berraud-Pache, Attila Tajti, Péter G. Szalay
In Table 2 the limiting values for ammonia–oxygen-difluoride are shown. The same pattern is seen here as in case of the ammonia-fluorine system, the errors and deviations are even numerically very similar. Thus we see substantial size extensivity errors for CCSD, CCSD(2), and CC2, while almost negligible ones for the triples methods, except CC3 where it is now almost −0.1 eV. While CCSD overestimates the limiting value, CC2 underestimates it by large, in line with the finding on the CT excitation energies at equilibrium distances [1]. The larger size extensivity error of CC3 is due to the underestimation of the limiting values, since the IP and EA values are nearly perfect. Note that in Ref. [1] CC3 showed the largest error for this molecule, a finding which is partly explained now.
Excitation spectra of fully correlated donor-acceptor complexes by density matrix renormalisation group
Published in Molecular Physics, 2023
Gergely Barcza, Anton Pershin, Adam Gali, Örs Legeza
It is known that the efficiency of the DMRG depends significantly on the choice of basis [65–69]. Therefore, to further highlight this effect and the robustness of the method we performed calculations by using two basis sets and by choosing M values that lead to a similar overall scaling as the reference CC methods. Fixing and the bare DMRG results with overall scaling of can be compared to CCSD(T) () and CCSDT (). The results for ammonia-fluorine and ammonia-oxygen difluoride are summarised in Table 3 for the canonical HF orbitals and for localised orbitals obtained by the Foster-Boys localisation protocol [70]. It is clearly visible that localised orbitals lead to significant improvements, i.e. the ground state energy of ammonia-fluorine is lowered by some 50 mHa for the given M. The LE excitation energies also decrease by ∼0.1 eV towards the CCSDT solution. Most strikingly, the localised basis improves the description of CT excitation energy by 0.47 eV. A further increase in the bond dimension to leads to the consistent excitation spectra by CCSDT and DMRG, exhibiting the energy differences below 0.05 eV. The ground state energy by DMRG is even lower than by CCSDT by ∼8 mHa and it is in good agreement with the extrapolated value in Table 1. Similarly, for the larger ammonia-oxygen difluoride complex, the choice of also provides an excellent agreement between DMRG and CCSDT results with the energy difference ∼0.05 eV. Noteworthy, we again observe a large improvement of the CT state energy (7.04 eV by CCSDT) due to localisation.