341 research outputs found
(S)-(−)-1-Phenylethanaminium 4-(4,4-difluoro-1,3,5,7-tetramethyl-3a,4a-diaza-4-borata-s-indacen-8-yl)benzoate
The title compound, C8H12N+·C20H18BF2N2O2
−, crystallizes with a significant amount of void space [4.0 (5)%] in the unit cell. The structure displays N—H⋯O hydrogen bonding between the components. The plane formed by the benzoic acid moiety of the BODIPY-CO2
− is twisted by 80.71 (6)° relative to the plane formed by the ring C and N atoms of the tetramethyldipyrrin portion of the molecule
M–M Bond-Stretching Energy Landscapes for M_2(dimen)_(4)^(2+) (M = Rh, Ir; dimen = 1,8-Diisocyanomenthane) Complexes
Isomers of Ir_2(dimen)_(4)^(2+) (dimen = 1,8-diisocyanomenthane) exhibit different Ir–Ir bond distances in a 2:1 MTHF/EtCN solution (MTHF = 2-methyltetrahydrofuran). Variable-temperature absorption data suggest that the isomer with the shorter Ir–Ir distance is favored at room temperature [K = ~8; ΔH° = −0.8 kcal/mol; ΔS° = 1.44 cal mol^(–1) K^(–1)]. We report calculations that shed light on M_2(dimen)_(4)^(2+) (M = Rh, Ir) structural differences: (1) metal–metal interaction favors short distances; (2) ligand deformational-strain energy favors long distances; (3) out-of-plane (A_(2u)) distortion promotes twisting of the ligand backbone at short metal–metal separations. Calculated potential-energy surfaces reveal a double minimum for Ir_2(dimen)_(4)^(2+) (4.1 Å Ir–Ir with 0° twist angle and ~3.6 Å Ir–Ir with ±12° twist angle) but not for the rhodium analogue (4.5 Å Rh–Rh with no twisting). Because both the ligand strain and A_(2u) distortional energy are virtually identical for the two complexes, the strength of the metal–metal interaction is the determining factor. On the basis of the magnitude of this interaction, we obtain the following results: (1) a single-minimum (along the Ir–Ir coordinate), harmonic potential-energy surface for the triplet electronic excited state of Ir_2(dimen)_(4)^(2+) (R_(e,Ir–Ir) = 2.87 Å; F_(Ir–Ir) = 0.99 mdyn Å^(–1)); (2) a single-minimum, anharmonic surface for the ground state of Rh_2(dimen)_(4)^(2+) (R_(e,Rh–Rh) = 3.23 Å; F_(Rh–Rh) = 0.09 mdyn Å^(–1)); (3) a double-minimum (along the Ir–Ir coordinate) surface for the ground state of Ir_2(dimen)_(4)^(2+) (R_(e,Ir–Ir) = 3.23 Å; F_(Ir–Ir) = 0.16 mdyn Å^(–1))
Beable-Guided Quantum Theories: Generalising Quantum Probability Laws
We introduce the idea of a {\it beable-guided quantum theory}. Beable-guided
quantum theories (BGQT) are generalisations of quantum theory, inspired by
Bell's concept of beables. They modify the quantum probabilities for some
specified set of fundamental events, histories, or other elements of
quasiclassical reality by probability laws that depend on the realised
configuration of beables. For example, they may define an additional
probability weight factor for a beable configuration, independent of the
quantum dynamics.
BGQT can be fitted to observational data to provide foils against which to
compare explanations based on standard quantum theory. For example, a BGQT
could, in principle, characterise the effects attributed to dark energy or dark
matter, or any other deviation from the predictions of standard quantum
dynamics, without introducing extra fields or a cosmological constant. The
complexity of the beable-guided theory would then parametrise how far we are
from a standard quantum explanation.
Less conservatively, we give reasons for taking suitably simple beable-guided
quantum theories as serious phenomenological theories in their own right. Among
these are that cosmological models defined by BGQT might in fact fit the
empirical data better than any standard quantum explanation, and that BGQT
suggest potentially interesting non-standard ways of coupling quantum matter to
gravity.Comment: Minor corrections and edits; closer but not identical to published
versio
Bohmian Histories and Decoherent Histories
The predictions of the Bohmian and the decoherent (or consistent) histories
formulations of the quantum mechanics of a closed system are compared for
histories -- sequences of alternatives at a series of times. For certain kinds
of histories, Bohmian mechanics and decoherent histories may both be formulated
in the same mathematical framework within which they can be compared. In that
framework, Bohmian mechanics and decoherent histories represent a given history
by different operators. Their predictions for the probabilities of histories
therefore generally differ. However, in an idealized model of measurement, the
predictions of Bohmian mechanics and decoherent histories coincide for the
probabilities of records of measurement outcomes. The formulations are thus
difficult to distinguish experimentally. They may differ in their accounts of
the past history of the universe in quantum cosmology.Comment: 7 pages, 3 figures, Revtex, minor correction
Tetra-n-butylammonium bis(1,1-dicyanoethylene-2,2-dithiolato)platinum(II)
In the title compound, (C16H36N)2[Pt(C4N2S2)2], the PtII center adopts a distorted square-planar geometry due to the 4-membered chelate rings formed by coordination to the S atoms of the 1,1-dicyanoethylene-2,2-dithiolate (i-mnt) ligands [bite angle 74.35 (4)°]. The bond distances in the coordinated i-mnt ligands indicate some delocalization of the π-system
The Status of the Wave Function in Dynamical Collapse Models
The idea that in dynamical wave function collapse models the wave function is
superfluous is investigated. Evidence is presented for the conjecture that, in
a model of a field theory on a 1+1 lightcone lattice, knowing the field
configuration on the lattice back to some time in the past, allows the wave
function or quantum state at the present moment to be calculated, to arbitrary
accuracy so long as enough of the past field configuration is known.Comment: 35 pages, 11 figures, LaTex, corrected typos, some modifications
made. to appear in Found. of Phys. Lett. Vol. 18, Nbr 6, Nov 2005, 499-51
Information measures and classicality in quantum mechanics
We study information measures in quantu mechanics, with particular emphasis
on providing a quantification of the notions of classicality and
predictability. Our primary tool is the Shannon - Wehrl entropy I. We give a
precise criterion for phase space classicality and argue that in view of this
a) I provides a measure of the degree of deviation from classicality for closed
system b) I - S (S the von Neumann entropy) plays the same role in open systems
We examine particular examples in non-relativistic quantum mechanics. Finally,
(this being one of our main motivations) we comment on field classicalisation
on early universe cosmology.Comment: 35 pages, LATE
Quantum Physics and Human Language
Human languages employ constructions that tacitly assume specific properties
of the limited range of phenomena they evolved to describe. These assumed
properties are true features of that limited context, but may not be general or
precise properties of all the physical situations allowed by fundamental
physics. In brief, human languages contain `excess baggage' that must be
qualified, discarded, or otherwise reformed to give a clear account in the
context of fundamental physics of even the everyday phenomena that the
languages evolved to describe. The surest route to clarity is to express the
constructions of human languages in the language of fundamental physical
theory, not the other way around. These ideas are illustrated by an analysis of
the verb `to happen' and the word `reality' in special relativity and the
modern quantum mechanics of closed systems.Comment: Contribution to the festschrift for G.C. Ghirardi on his 70th
Birthday, minor correction
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