1,721,284 research outputs found
High Resolution Free Jet Millimeter Wave Absorption Spectroscopy: a bridge to Astrochemistry
No full textConventional absorption spectroscopy is still the workhorse in high-resolution rotational laboratory spectroscopy.1 The data obtained from these kind of instruments are relevant for astronomical searches of complex molecules that represent excellent probes of the physical and chemical environments and history of the sources where they are detected.2 Nowadays, observations performed by the Atacama Large Millimeter Array (ALMA) open up new opportunities to reveal the chemical complexity of solar systems analogues. At the same time the huge amount of data collected and the extremely rich surveys represent a challenge for the astrochemistry community. The chance to detect molecules with an increasing large number of atoms, goes hand in hand with the complexity of their conformational equilibria, often associated with large amplitude motions, that need to be analysed in laboratory before taking on an astronomical search. For this reason a strong interplay between the laboratory spectroscopists and the observational astronomers is increasingly required to be able to unravel the spectra, which are rather difficult to predict theoretically, mainly in the sub-mm wave region.
In this talk laboratory results on diols and thiols of potential astronomical interest, obtained using the only Free Jet Absorption Millimeter Wave (FJAMMW) spectrometer working at the University of Bologna,3 will be presented. The rotational spectra (59.6 - 74.4 GHz, corresponding to 5.03 - 4.03 mm) reveal the presence of six conformers for 1,2-butanediol (C4H10O2) and four conformers for 1,3-propanedithiol (C3H8S2), proving the complexity of the conformational landscapes of these kind of compounds.
Moreover, taking advantage of the existing public ALMA data, some considerations on the rich molecular line spectrum of the Class 0 protostellar binary IRAS 16293-2422 will be discussed. References
[1] S. Brünken, S. Schlemmer, arXiv:1605.07456, 2016
[2] E. Herbst, E. F. van Dishoeck, Annu. Rev. Astron. Astrophys. 47, 427, 2009
[3] C. Calabrese, A. Maris, L. Evangelisti, L. B. Favero, S. Melandri, W. Caminati, J. Phys. Chem. A. 117, 13712, 201
High-Resolution Spectroscopic Studies of Complexes Formed by Medium-Size Organic Molecules
No full textA wealth of structural and dynamical information has been obtained in the last 30 years from the study of high-resolution spectra of molecular clusters generated in a cold supersonic expansion by means of highly resolved spectroscopic methods. The data obtained, generally lead to determination of the structures of stable conformations. In addition, in the case of weakly bound molecular complexes, it is usual to observe the effects of internal motions due to the shallowness of the potential energy surfaces involved and the flexibility of the systems. In the case of electronic excitation experiments, also the effect of electronic distribution changes on both equilibrium structures and internal motions becomes accessible. The structural and dynamical information that can be obtained by applying suitable theoretical models to the analysis of these unusually complex spectra allows the determination and understanding of the driving forces involved in formation of the molecular complex. In this way, many types of non-covalent interactions have been characterized, from pure van der Waals interactions in complexes of rare gases to moderate-strength and weak hydrogen bonds and to the most recent halogen bonds and n-π interactions. The aim of this review is to underline how the different experimental and theoretical methods converge in giving a detailed picture of weak interactions in small molecular adducts involving medium-size molecules. The conclusions regarding geometries and energies can contribute to understanding of the different driving forces involved in the dynamics of the processes and can be exploited in all fields of chemistry and biochemistry, from design of new materials with novel properties to rational design of drugs
Ring fluorination effects on molecular water clusters: the cases of 2-fluoropyridine, 3-fluoropyridine and penta-fluoropyridine. A rotational spectroscopy study.
No full textThe importance of organic fluorinated compounds in science and in everyday life is growing year after year.1 The effects of fluorination are related to the high electronegativity of this atom and its polarizability. In general the introduction of a fluorine atom is used in order to modulate physicochemical properties, like hydrophilicity and lipophilicity, of bio-organic molecules and functional materials.1,2 Additionally, structural changes can also be related to the electronic effect of the fluorine atom or to the molecule capability of creating new hydrogen bonds or non-covalent bonds, having fluorine as acceptor.
For this reason we investigate clusters where a molecule of water is used as a probe to reveal the changes on the electrostatic potential on the fluorinated compounds.
The experimental conditions are achieved in supersonic expansions using Molecular Beam Fourier Transform Microwave Spectroscopy technique (MBFTMW).3 The high resolution and sensitivity of rotational spectroscopy give direct access to the structural arrangement of the systems, allowing the measurement of bond lengths and angles. Moreover this gas phase technique allows unveiling subtle structural and dynamical effects usually related to changes in non-covalent interactions.
The series of clusters studied between different fluorinated pyridines and a molecule of water are: 2-fluoropyridine-water, 3-fluoropyridine-water and penta-fluoropyridine-water (see Figure 1) complexes. The results clearly show that the introduction of a single fluorine atom into a molecule already induces significant effects, but as the number of fluorine atoms increases, such as in the case of penta-fluoropyridine, the system starts to behave as a completely novel species.4 The perfluorination effect is clearly observable in the penta-fluoropyridine-water adduct where the water oxygen lone pairs point towards the aromatic ring.
Figure 1: the observed adducts of 2-fluoropyridine, 3-fluoropyridine and penta-fluoropyridine with a molecule of water
Call for papers for special issue of Journal of Molecular Spectroscopy focusing on ”Spectroscopy and Inter/Intramolecular Dynamics in Honor of Walther Caminati”
No full textNo Abstract -Editoria
Internal motions of the rare gas atom in dimethyl ether-krypton
No full textThe free jet millimeter-wave absorption spectra of two isotopomers of the weakly bonded dimethyl ether-Kr complex have been assigned and measured. The Kr atom lies in the óV symmetry plane of dimethyl ether perpendicular to the COC plane, at a r0-distance of 3.67 Å from its center of mass (cm). The line connecting the krypton atom to cm forms an r0-angle of 70° with the O-cm line. The observed conformation is in agreement with the global minimum as found with a distributed polarizability model. Many rotational transitions are split into two component lines, due to the motion of Kr relative to dimethyl ether in the complex. The corresponding splitting has been used to determine the barrier to the internal motion. Information on the dissociation energy has been deduced from the centrifugal distortion effects
Reference data for isolated trifluoroacetic acid
No full textThe dataset includes experimental rotational spectroscopy data and numerical data from computational simulations for the vibrational ground state of trifluoroacetic acid (TFA). The following information is provided: (i) quantum mechanical calculations at the MP2/aug-cc-pVTZ level for vibrational anharmonic force field and electric dipole moment determination and (ii) input and output files for the fitting of the experimental rotational transition lines of TFA with the CALPGM suit of programs. Fittings include more than 180 new spectral lines recorded at room temperature in the frequency range of 18-26 GHz using a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer and also incorporate spectroscopic data from previous studies (V. Stolwijk, B. van Eijck,Journal of Molecular Spectroscopy 113 (1) (1985) 196–207;S. Antolinez, J. L. Alonso, H. Dreizler, D. H. Sutter, Zeitschrift für Naturforschung A 54 (8-9) (1999) 524–538; B. Ouyang, T. G. Starkey, B. J. Howard, The Journal of Physical Chemistry A 111 (28) (2007) 6165–6175). Two fitting models are proposed, using Watson's S-reduction and -reduction in the Ir representation, leading to the refinement of the molecular parameters
Millimeter wave spectroscopy of flexible molecules relevant to astrochemistry
No full textThe investigation of phenomena related to the chemistry of the Cosmos is strongly based on the identification of molecules by spectroscopic methods and a knowledge of their spectroscopic parameters or their transition frequencies is needed. Rotational spectroscopy, with its high resolution, is the most powerful tool for the unambigous identification of molecules and laboratory work is needed to provide the community with the spectral features to analyze the cosmological surveys.
Many of the molecules detected in space are complex organic molecules containing chains of carbon atoms and which therefore show a high degree of molecular flexibility. The high number of low energy conformations and the presence of large amplitude motions on shallow potential energy surfaces are peculiar to this kind of systems. The presence of a high number of stable conformers - often interconverting through small energy barriers - usually gives rise to very complex rotational spectra, which represent a challenge for spectroscopic and computational methods.
Spectroscopic strategies for the rotational study of flexible molecules include the use of the cold and isolated conditions of a free jet expansion and laser ablation sources for the non volatile systems while the computational methods must deal with complex conformational surfaces and large amplitude motions which can be coupled to the overall rotation causing a hyperfine splitting of the rotational transitions.
We will give examples of rotational spectroscopy of highly flexible organic molecules of astrophysical interest studied by the Free Jet Spectroscopy Group in Bologna with instruments going from 6 to 78 GHz. They include methylacetate [1], methylaminoethanol and biological building blocks like C4 sugars [2] The interpretation of their rotational spectra with appropriate models is essential to correctly predict their spectral features at higher frequencies.
[1] M. Tudorie, I. Kleiner, J. T. Hougen, S. Melandri, L. W. Sutikdja, W. Stahl, J. Mol. Spectr., 269, 211 (2011)
[2] B. M. Giuliano, S. Blanco, S. Melandri, and W. Caminati, Astrophy. J. Suppl,.179, 355 (2008); B. M. Giuliano, S. Blanco, S. Melandri, W. Caminati, Chem. Phys. Lett., 467, 74 (2008
Conformational data of 3-chloropropionic acid
No full textThe conformational space of 3-chloropropionic acid was explored using computational methods and the three obtained conformers have been optimized at b3lyp-d3(bj)/def2tzvp level of calculations and the minima have been verified by frequency calculations. The fits obtained through SPFIT/SPCAT for the rotational spectrum of the various conformers are reported. For each conformers have been observed the most abundant isomers and its chlorine-37 isotopologues in natural abundance
High Resolution Millimeter Wave Absorption Spectroscopy: from the laboratory data to the astronomical surveys
No full textConventional absorption spectroscopy is still the workhorse in high-resolution rotational laboratory spectroscopy.1 The data obtained from these kind of instruments are relevant for astronomical searches of complex molecules that represent excellent probes of the physical and chemical environments and history of the sources where they are detected.2 Nowadays, observations performed by the Atacama Large Millimeter Array (ALMA) open up new opportunities to reveal the chemical complexity of solar systems analogues. At the same time the huge amount of data collected and the extremely rich surveys represent a challenge for the astrochemistry community. To reach this goal, the spectroscopic know-how is fundamental in recognizing typical pattern lines due to multiple internal interactions and motions that cause complicated energy level schemes, since the resulting spectra will be rather difficult to predict theoretically, mainly in the sub-mm wave region. For this reason a strong interplay between laboratory spectroscopists and observational astronomers is increasingly required to be able to unravel the experimental data.
In this talk the features and the potential of the high resolution rotational spectroscopy technique will be pointed out, providing some results on different kind of molecules characterized by complex conformational landscapes. In particular, molecular spectra of potential astronomical interest will be presented, obtained using the free jet absorption millimeter wave and the free space cell absorption sub-mm wave spectrometers working at University of Bologna.3
References
[1] S. Brünken, S. Schlemmer, arXiv:1605.07456, 2016
[2] E. Herbst, E. F. van Dishoeck, Annu. Rev. Astron. Astrophys. 47, 427, 2009
[3] C. Calabrese, A. Maris, L. Evangelisti, L. B. Favero, S. Melandri, W. Caminati, J. Phys. Chem. A. 117, 13712, 201
Conformational preferences of molecules, biomolecules and molecular complexes: the importance of the hydrogen bond and other non-bonding interactions
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