163 research outputs found
Rotational investigation of the adducts of formic acid with alcohols, ethers and esters
Mixtures of formic acid with methyl alcohol, with isopropyl alcohol, with \textit{tert}-butyl alcohol, with dimethylether
and with isopropylformiate have been supersonically expanded as pulsed jets. The obtained cool plumes have been
analyzed by Fourier transform microwave spectroscopy. It has been possible to assign the rotational spectra
of the 1:1 adducts of formic acid with \textit{tert}-butyl alcohol, with dimethyl ether and with isopropylformiate.
The conformational shapes and geometries of these adducts, as well as the topologies of their itermolecular hydrogen
bonds will be presented.
An explanation is given of the failure of the assignments of the rotational spectra of the adducts of formic acid with
methyl alcohol and isopropyl alcohol
THE ROTATIONAL SPECTRUM OF PYRIDINE-FORMIC ACID
The rotational spectrum of three 1:1 complexes of pyridine with formic acid has been observed and assigned using pulsed jet Fourier transform microwave technique. The two subunits are held together through one O-H���N hydrogen bond and one C-H���O weak hydrogen bond, forming a seven-membering cyclic structure. The rotational spectrum of the pyridine-HCOOD isotopologue is considerably shifted towards lower frequencies, with respect to the "rigid" model, suggesting a considerable Ubbelohde effect, similar in nature to that observed in the bi-molecules of carboxylic acids
The LAM of the Rings: Large Amplitude Motions in Aromatic Molecules Studied by Microwave Spectroscopy
Large amplitude motions (LAMs) form a fundamental phenomenon that demands the development of specific theoretical and Hamiltonian models. In recent years, along with the strong progress in instrumental techniques on high-resolution microwave spectroscopy and computational capacity in quantum chemistry, studies on LAMs have become very diverse. Larger and more complex molecular systems have been taken under investigation, ranging from series of heteroaromatic molecules from five-and six-membered rings to polycyclic-aromatic-hydrocarbon derivatives. Such systems are ideally suited to create families of molecules in which the positions and the number of LAMs can be varied, while the heteroatoms often provide a sufficient dipole moment to the systems to warrant the observation of their rotational spectra. This review will summarize three types of LAMs: internal rotation, inversion tunneling, and ring puckering, which are frequently observed in aromatic five-membered rings such as furan, thiophene, pyrrole, thiazole, and oxazole derivatives, in aromatic six-membered rings such as benzene, pyridine, and pyrimidine derivatives, and larger combined rings such as naphthalene, indole, and indan derivatives. For each molecular class, we will present the representatives and summarize the recent insights on the molecular structure and internal dynamics and how they help to advance the field of quantum mechanics
On the weak O-H⋯halogen hydrogen bond: A rotational study of CH 3CHClF⋯H2O
We measured the molecular beam Fourier transform microwave spectra of six isotopologues of the 1:1 adduct of CH3CHClF with water. Water prefers to form an O-H⋯F rather than an O-H⋯Cl hydrogen bond. This is just the contrary of what was observed in the chlorofluoromethane-water adduct, where an O-H⋯Cl link was formed (W. Caminati, S. Melandri, A. Maris and P. Ottaviani, Angew. Chem., Int. Ed., 2006, 45, 2438). The water molecule is linked with an O-H⋯F bridge to the fluorine atom, with r(F⋯H w) = 2.14 Å, and with two C-H⋯O contacts to the alkyl hydrogens with r(C1-H1⋯Ow) = 2.75 Å and r(C2-H2⋯Ow) = 2.84 Å, respectively. Besides the rotational constants, the quadrupole coupling constants of the chlorine atom have been determined. In addition, information on the internal dynamics has been obtained. © the Owner Societies 2011
Furanosic forms of sugars: conformational equilibrium of methyl beta-D-ribofuranoside
The investigation of an isolated ribofuranose unit in the gas phase
reveals the intrinsic conformational landscape of the biologically
active sugar form.We report the rotational spectra of two conformers
of methyl b-D-ribofuranoside in a supersonic jet expansion. Both
conformers adopt a near twisted (3T2) ring conformation with the
methoxy and hydroxymethyl substituents involved in various intramolecular
hydrogen bonds.MINECO-FEDER CTQ2015-68148-C2-
A butterfly motion of formic acid and cyclobutanone in the 1:1 hydrogen bonded molecular cluster
Producción CientíficaUpon supersonic expansion, formic acid and cyclobutanone (CBU) form a molecular cluster in which the two constituent molecules, linked by OH⋯O and CH⋯O hydrogen bonds, undergo a rapid interconversion between two equivalent forms. The tunneling motion takes place through the rupture and reformation of the C–H⋯O hydrogen bond between the carbonyl oxygen of HCOOH and one of the two hydrogen atoms of the methylenic group adjacent to the cyclobutanone keto group. From the microwave spectra, tunneling energy splittings (ΔE01) have been determined for the parent (1122.756(3) MHz), DCOOH⋯CBU (1084.538(1) MHz) and HCOOD⋯CBU (1180.282(4) MHz) isotopic species. From these splittings, the potential barrier to interconversion has been calculated to be B2 = 39.7(5) cm−1. The tunneling pathway is an asymmetric butterfly-like motion between the two moieties of the adduct, with a barrier at a configuration in which the ring plane of cyclobutanone is coplanar with formic acid.Ministerio de Economía, Industria y Competitividad (CTQ2015- 68148-C2-2-P)Junta de Castilla y León (programa de apoyo a proyectos de investigación – (UNVA-13-3E-2103)Italian MIUR (PRIN project 2010ERFKXL_001
Amplification of polarization NOON states
NOON states are path entangled states which can be exploited to enhance phase
resolution in interferometric measurements. In the present paper we analyze the
quantum states obtained by optical parametric amplification of polarization
NOON states. First we study, theoretically and experimentally, the
amplification of a 2-photon state by a collinear Quantum Injected Optical
Parametric Amplifier (QIOPA). We compared the stimulated emission regime with
the spontaneous one, studied by Sciarrino et al. (PRA 77, 012324), finding
comparable visibilities between the two cases but an enhancement of the signal
in the stimulated case. As a second step, we show that the collinear amplifier
cannot be successfully used for amplifying N-photon states with N>2 due to the
intrinsic \lambda/4 oscillation pattern of the crystal. To overcome this
limitation, we propose to adopt a scheme for the amplification of a generic
state based on a non-collinear QIOPA and we show that the state obtained by the
amplification process preserves \lambda/N feature and exhibits a high
resilience to losses. Furthermore, an asymptotic unity visibility can be
obtained when correlation functions with sufficiently high order M are
analyzed.Comment: 10 pages, 9 figure
Electron penetration in the nucleus and its effect on the quadrupole interaction
A series expansion of the interaction between a nucleus and its surrounding
electron distribution provides terms that are well-known in the study of
hyperfine interactions: the familiar quadrupole interaction and the less
familiar hexadecapole interaction. If the penetration of electrons into the
nucleus is taken into account, various corrections to these multipole
interactions appear. The best known one is a scalar correction related to the
isotope shift and the isomer shift. This paper discusses a related tensor
correction, which modifies the quadrupole interaction if electrons penetrate
the nucleus: the quadrupole shift. We describe the mathematical formalism and
provide first-principles calculations of the quadrupole shift for a large set
of solids. Fully relativistic calculations that explicitly take a finite
nucleus into account turn out to be mandatory. Our analysis shows that the
quadrupole shift becomes appreciably large for heavy elements. Implications for
experimental high-precision studies of quadrupole interactions and quadrupole
moment ratios are discussed. A literature review of other small quadrupole-like
effects is presented as well
Non Covalent Interactions And Internal Dynamics In Adducts Of Freons
The complexation of chlorofluorocarbons (CFCs) with atmospheric water and pollutants of the atmosphere affects their reactivity and it seems to accelerate, for example, the decomposition rate of freons in the atmosphere [1]. For this reason we characterized shapes, stabilities, nature of the non-covalent interactions, structures and internal dynamics of a number of complexes of CFCs with water and of their dimers or oligomers by rotational spectroscopy.
It has been found that hydrogenated CFCs form adducts with other molecules through weak hydrogen bonds (WHBs). Their C-H groups can act as proton donors, enhanced by the electron withdrawing of the halogen atoms, interacting with the electron rich regions of the partner molecules [2]. Also in adducts or oligomers of hydrogenated CFCs the monomer units are held together by nets of WHBs [3]. When CFCs are perhalogenated, the positive electrostatic region (“-hole”) can interact electrostatically with negative sites of another, or of the same molecular entity, giving rise, according to IUPAC, to the so called halogen bond (HaB). However, it has been observed that when the perhalogenated CFCs has a electron system, a lone pair••• interaction (Bürgi-Dunitz) is favoured [4].
We describe here the HaBs that CF and CFCl form with a variety of partner molecules such as water, ammonia, dimethyl ether, etc. Important spectroscopic features outline strong dynamics effects taking place in this kind of complex.
References
[1] V. Vaida, H. G. Kjaergaard, K. J. Feierabend, Int. Rev. Phys. Chem. 22 (2003) 203.
[2] See, for example: W. Caminati, S. Melandri, A. Maris, P. Ottaviani, Angew. Chem. Int. Ed. 45 (2006) 2438.
[3] G. Feng, L. Evangelisti, I. Cacelli, L. Carbonaro, G. Prampolini, W. Caminati, Chem. Commun. 50 (2014) 171.
[4] Q. Gou, G. Feng, L. Evangelisti, W. Caminati, Angew. Chem. Int. Ed. 52 (2013) 52 11888
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