1,721,084 research outputs found
Rotational spectra of rare isotopic species of fluoroiodomethane:Determination of the equilibrium structure from rotational spectroscopy and quantum-chemical calculations
No full textSupported by accurate quantum-chemical calculations, the rotational spectra of the mono- and bi-deuterated species of fluoroiodomethane, CHDFI and CD2FI, as well as of the 13C-containing species, 13CH2FI, were recorded for the first time. Three different spectrometers were employed, a Fourier-transform microwave spectrometer, a millimeter/submillimter-wave spectrometer, and a THz spectrometer, thus allowing to record a huge portion of the rotational spectrum, from 5 GHz up to 1.05 THz, and to accurately determine the ground-state rotational and centrifugal-distortion constants. Sub-Doppler measurements allowed to resolve the hyperfine structure of the rotational spectrum and to determine the complete iodine quadrupole-coupling tensor as well as the diagonal elements of the iodine spin-rotation tensor. The present investigation of rare isotopic species of CH2FI together with the results previously obtained for the main isotopologue [C. Puzzarini, G. Cazzoli, J. C. López, J. L. Alonso, A. Baldacci, A. Baldan, S. Stopkowicz, L. Cheng, and J. Gauss, J. Chem. Phys. 134, 174312 (2011); G. Cazzoli, A. Baldacci, A. Baldan, and C. Puzzarini, Mol. Phys. 109, 2245 (2011)] enabled us to derive a semi-experimental equilibrium structure for fluoroiodomethane by means of a least-squares fit procedure using the available experimental ground-state rotational constants together with computed vibrational corrections. Problems related to the missing isotopic substitution of fluorine and iodine were overcome thanks to the availability of an accurate theoretical equilibrium geometry (computed at the coupled-cluster singles and doubles level augmented by a perturbative treatment of triple excitations)
Hyperfine structure of rotational spectra: interplay of experiment and theory
No full textThe determination of (hyper)fine parameters such as quadrupole-coupling, spin-spin coupling, and spin-rotation constants is one of the aims of high-resolution rotational spectroscopy. These parameters are relevant not only from a spectroscopic point of view, but also from a physical and/or chemical viewpoint, as they might provide detailed information on the chemical bond, structure, etc. Furthermore, the hyperfine structure of rotational spectra is so characteristic that its analysis may help in assigning the spectra of unknown species [1].
However, the experimental determination of hyperfine constants can be a challenge not only for actual problems in resolving hyperfine structures themselves, but also due to the lack of reliable estimates or the complexity of the hyperfine structure itself. It is thus important to be
able to rely on good predictions for such parameters, which can nowadays be provided by quantum-chemical calculations [2]. In fact, the aim of this presentation is to show how fruitful the interplay between experiment and theory can be in this field. A number of examples will be presented to illustrate this interplay in the investigation of hyperfine structures of rotational spectra. Those include isotopic species of water and formic acid as well as heavy-element containing species, as CH2FI.
From an experimental point of view, we focus on the Lamb-dip technique. This technique allows to improve the resolving power in the millimeter- and submillimeter-wave frequency range by at least one order of magnitude, thus making it possible to perform sub-Doppler measurements as well as to resolve narrow hyperfine structures. In particular, the high resolution that can be achieved by our experimental set up will be demonstrated by a few representative examples [3,4].
Concerning theory, the theoretical background for the required quantum-chemical calculations will be briefly reviewed, and a particular emphasis on the computational requirements will be given [2]. It will be demonstrated that high-level calculations can provide very reliable values for hyperfine parameters (quadrupole coupling constants, spinrotation tensors, spin-spin couplings, etc.) and how theoretical predictions are often essential for a detailed analysis of the hyperfine structure of the recorded spectra [5].
[1] G. Cazzoli, C. Puzzarini, A. Gambi, J. Chem. Phys. 120 (2004) 6495-6501.
[2] C. Puzzarini, J. F. Stanton, J. Gauss, Int. Rev. Phys. Chem. 29 (2010) 273-367.
[3] G. Cazzoli, C. Puzzarini, J. Mol. Spectrosc. 226 (2004) 161-168.
[4] G. Cazzoli, L. Dore, C. Puzzarini, Astron. Astrophys. 507 (2009) 1707-1710.
[5] C. Puzzarini, G. Cazzoli, M. E. Harding, J. Vázquez, J. Gauss, J. Chem. Phys. 131 (2009) 234304/1-11
Lamb-dip spectrum of methylacetylene and methyldiacetylene: precise rotational transition frequencies and parameters of the main isotopic species
No full textContext. Methylacetylene and methyldiacetylene are the first members of the methylpolyynes series, CH3C2nH (n = 1, 2). Their astrophysical relevance has motivated this spectroscopic study.
Aims. The aim of this investigation is to provide very accurate rest frequencies, as well as to improve the spectroscopic parameters
available in the literature for these molecules.
Methods. The Lamb-dip technique was exploited in order to record the rotational spectra of CH3CCH and CH3CCCCH at sub-Doppler resolution in the millimeter- and submillimeter-wave frequency ranges. In addition, for CH3CCH rotational transitions in the THz region were recorded at Doppler resolution.
Results. We report the most accurate ground-state rotational parameters known at the moment for the main isotopic species of methylacetylene, as well as of methyldiacetylene.
Conclusions. Since both molecules are known to be of astrophysical relevance, we are confident that the improvement in the accuracy
of the ground-state rotational parameters as well as of the rest frequencies of rotational transitions could be useful for future
observations purposes
Determination of the molecular dipole moment of bromofluoromethane: microwave stark spectra and ab initio calculations
No full textThe electric dipole moment of bromofluoromethane, CH2
(79)BrF, has been determined with a good accuracy by observing the second
order DMJ = 0 Stark spectrum of the J = 3,2,1 ‹- 3,1,2, J = 5,2,3 ‹- 5,1,4 and J = 5,2,4 ‹- 5,1,5 rotational transitions. In addition, the equilibrium
geometry and dipole moment have been evaluated using highly accurate ab initio calculations. By comparing the experimental
[mua = 0.3466(11) D and mub = 1.704(26) D] and theoretical [mua = -0.339 D and mub = -1.701 D] dipole moment components, a very good
agreement has been found
Setup of a 1D Model for Simulating Dynamic Behaviour of Motorcycle Forks
No full textShock absorbers and damper systems are important parts of automobiles and motorcycles because they have effects on safety, ride comfort, and handling. In particular, for vehicle safety, shock absorber system plays a fundamental role in maintaining the contact between tire and road. Generally, to assure the best trade-off between safety and ride comfort, a fine experimental tuning on all shock absorber components is necessary. Inside a common damper system the presence of several conjugated actions made by springs, oil and pressurized air requires a significant experimental support and a great number of prototypes and test. Aimed to reduce the design and tuning phases of a damper system, it is necessary to join these phases together with a numerical modelling phase.
The aim of this paper is to present the development of a mono-dimensional (1D) model for simulating dynamic behaviour of damper system. In particular, a conventional telescopic fork produced by PAIOLI MECCANICA has been considered as testing bench. It is important to underline that the same approach could be used to simulate the dynamic behaviour of an automobile shock absorber system. Fork numerical modelling has to assure a faster design process and a performance optimisation, reducing at the same time, the design time between the product idea and its final assembly. PAIOLI MECCANICA had the necessity of modelling its forks in order to quickly test different solutions and to improve actual fork performances. The present research concerns only fore-carriage forks for road applications, i.e. forks used in motorcycle not dedicated to races.
The fork model is developed in AMESim code using both hydraulic and pneumatic libraries. A sinusoidal displacement is directly impressed to the fork rod at different axial velocities (from 100 to 2000 mm/s) for simulating the axial excitation imposed to an actual fork by the road discontinuities. Numerical results are compared with experimental data recorded by PAIOLI MECCANICA. In particular, the fork numerical model demonstrates of being capable to reproduce the testing fields typically used as experimental test bench for motorcycle forks
Microwave spectrum of deuterated species of trans-1-chloro-2-fluoroethylene. Spectroscopic parameters and molecular structure from experiment and ab initio calculations
No full text
The hyperfine structure of the inversion-rotation transition J,K = 1,0 ← 0,0 of NH3 investigated by Lamb-dip spectroscopy
No full textThe ground-state inversion-rotation transition of ammonia at 572.498 GHz has been investigated in the laboratory using a source-modulation microwave spectrometer equipped with a double-pass cell. The experiment has been carried out at a pressure lower than 0.5 mTorr, thus enabling to record a Lamb-dip spectrum showing a partial resolution of the magnetic hyperfine structure due to the three proton spins. The achieved high resolution proved to be comparable to that of molecular beam experiments. This measurement provides very precise rest frequencies of the J,K = 1,0 ← 0,0 transition and of its hyperfine components, which fall in a spectral region covered by the HIFI instrument on board the Herschel satellite
Hyperfine structure in the rotational spectrum of trans-formic acid: Lamb-dip measurements and quantum-chemical calculations
No full textContext. Formic acid, HCOOH, is the simplest organic acid and the first that has been identified in the interstellar medium. Its astrophysical relevance has motivated this spectroscopic study.
Aims. The aim of this investigation is to provide very accurate rest frequencies for the trans isomer of HCOOH as well as to improve the spectroscopic and hyperfine parameters available in the literature for this molecule.
Methods. The Lamb-dip technique has been exploited in order to record the rotational spectrum of trans-HCOOH at sub-Doppler resolution in the millimeter- and submillimeter-wave frequency ranges and, when possible, to resolve the hyperfine structure due to the hydrogen nuclei. THz measurements have been carried out as well. The experimental investigation has been supported by high-level quantum-chemical calculations.
Results. As a consequence, we report here the most accurate ground-state rotational parameters known so far for the main isotopic species of trans-HCOOH as well as an accurate and reliable set of hyperfine parameters.
Conclusions. The improvement in the accuracy of the ground-state rotational and hyperfine parameters as well as of the rest frequencies of rotational transitions might therefore be useful for future radioastronomical observations
- …
