35,239 research outputs found
Millimeter And Sub-millimeter Spectroscopy Of Doubly Deuterated Acetaldehyde (cd2hcho)
No full textIn the last years the number of multi-deuterated molecules detected in the Interstellar Medium (ISM) increased substantially. These molecules are found to be more abundant than expected when taking into account the ISM deuterium abundance (D/H = 2.0 0.1 10, Drozdovskaya {\em et al.}\footnote{Drozdovskaya, M. N., Coudert, L. H., Margulès, L., Coutens, A., Jorgensen, J. K., Manigand, S., 2022, A\&A, in press} and references therein). In order to better understand the nature of deuterium fractionation, and the interplay of the chemistry in the gas phase and on the surface of dust grains, chemical models need to be constrained by observations of singly- and multi-deuterated molecules. Doubly deuterated acetaldehyde (CDHCHO) has not been detected in the ISM yet as it has been studied in the laboratory only up to 40 GHz (Turner Cox\footnote{Turner, P. H., Cox, A. P., 1976, Chem. Phys. Lett., 42, 1}, Turner {\em et al.}\footnote{Turner, P. H., Cox, A. P., Hardy, J. A., 1981, J. Chem. Soc., 77, 1217-1231}) and hence lacks an extensive spectroscopic study, in contrast with the singly-deuterated forms CHDCHO and CHCDO that were detected towards the protostellar core IRAS16293-2422B (Coudert {\em et al.}\footnote{Coudert, L. H., Margulès, L., Vastel, C., Motiyenko, R., Caux, E., Guillemin, J.-C., 2019, A\&A, 624, A70}). In order to allow the first detection of CDHCHO in the ISM, and to understand its deuterium fractionation, we are studying the rotational spectrum of CDHCHO in the millimetre and sub-millimeter frequency range.
This work should allow us to obtain an accurate spectral catalogue for CDHCHO, which we will use to search for this molecule in star-forming regions
Outsourcing and Skill Imports: Foreign High-Skilled Workers on H-1B and L-1 Visas in the United States
No full textThis working paper looks in detail at the H-1B and L-1 visa programs for temporary employment in the United States. Based on official data from the US Citizenship and Immigration Services and the US Department of State, H-1B and L-1 visa issuance rapidly increased in the late 1990s, followed by a marked slowdown after 2001. This points to the highly cyclical nature of both visa programs. Indian nationals and immigrants working in computer-related occupations dominate the H1-B and L-1 population in the United States, but these two groups are also found to be the most cyclical segment, with very large declines in inflows after 2001. The total population of H-1B visaholders in 2003 is estimated to range between 387,000 and 746,000, of which 160,000 to 306,000 were Indian nationals. As all data on H-1B/L-1 visaholders are gross numbers and gross jobs data for comparable categories are absent, the extent of the impact of these visa programs on the US labor market cannot be gauged precisely. A broad range of US industries and educational institutions are found to be employing H-1B recipients, with the IT industry being the dominant sector. Evidence of aggressive wage-cost cutting, including paying H-1B recipients only the legally mandated 95 percent of the prevailing US wage, is found among some H-1B employers, although no systematic abuse of the system is present.Outsourcing, offshoring, high-skilled labor, immigration, H1B/L-1 visas
GLOBAL ANALYSIS OF THE WATER MOLECULE SPECTRUM BEYOND THE SECOND TRIAD
No full textLanquetin, Coudert, and Camy-Peyret, J. Molec. Spectrosc. 195, 54 (1999); Lanquetin, Coudert, and Camy-Peyret, J. Molec. Spectrosc. 206, 83 (2001); and Coudert, Pirali, Vervloet, Lanquetin, and Camy-Peyret, J. Molec. Spectrosc. 2004, submitted. Bunker and Moss, J. Molec. Spectrosc. 80, 217 (1980). Partridge and Schwenke, J. Chem. Phys. 106, 4618 (1997).Author Institution: Laboratoire de Photophysique Mol\'{e}culaire, C.N.R.S., B\^{a}t. 350, Universit\'{e} Paris-SudThe spectrum of the water molecule has been the subject of a very large number of theoretical investigations. These are motivated by the importance of this molecule, by the availability of a large body of high-resolution data, and by the fact that it is a theoretically challenging molecule displaying a strong vibration-rotation coupling leading to an anomalous centrifugal distortion. In this paper, using the same ideas as in several previous in which satisfactory analyses of the water molecule rovibrational energy were performed up to the second triad, an effective rotation-vibration Hamiltonian will be built and used to account for the rovibrational energy of water up to the the first hexad. In agreement with Bunker and this effective rotation-vibration Hamiltonian is obtained starting from the exact Hamiltonian of the molecule written with Radau coordinates and adding the kinetic energy-like terms arising from the breakdown of the Born-Oppenheimer approximation. The effective Hamiltonian thereby obtained accounts for all three vibrational modes of the molecule and for the overall rotation. Making use of the potential energy function obtained by Partridge and the Schr\""{o}dinger equation for this effective Hamiltonian is then solved and rovibrational levels are obtained. In the paper, the theoretical formalism will be introduced and we hope to be able to show results concerning a global analysis of the rovibrational levels of water up to the first hexad
Hyperfine Coupling and Large Amplitude Motions Interaction in the Water Dimer
No full textExperimental and theoretical analyses of the hyperfine structure of the non-rigid water dimer (H2O)2 were carried out. Measurements
were performed with an FT-MW spectrometer allowing us to resolve most of the hyperfine components. Eight hyperfine patterns were
recorded involving rotational-tunneling sublevels with J 6 2. Hyperfine patterns were analyzed accounting for the magnetic spin–rotation
and spin–spin hyperfine couplings. Symmetry adapted nuclear spin wavefunctions were built to account for the interaction of the
hyperfine coupling with the large amplitude motions displayed by the water dimer and to build total rotational-tunneling-hyperfine wavefunctions
obeying the Pauli exclusion principle. This accounts for the strong dependence of the hyperfine patterns on the symmetry species
of the rotational-tunneling sublevels. These theoretical results were used to perform individual and global analyses of the hyperfine
patterns. The latter analysis yields values for some of the components of the spin–rotation coupling tensors
MAGNETIC SPIN-TORSION COUPLING IN METHANOL
No full textThe hyperfine structure of non-rigid molecules in which
hyperfine coupling arises from equivalent nuclei that can be
exchanged by large amplitude motions is of great interest and
lead to unexpected results. In the non-rigid (CD)
and (DO) dimers, the hyperfine structure arising for
nondegenerate tunneling sublevels can be accounted for using
an effective quadrupole coupling Hamiltonian with the same
coupling constant for all four deuterium atoms.footnote{Bhattacharjee, Muenter, and Coudert, {em
J. Chem. Phys.}~{bf 97} (1992) 8850; and Stahl and
Coudert, {em J. Mol. Spectrosc.}~{bf 157} (1993) 161.}
In the non-rigid species CDCOH and HCOOCH, the large
amplitude torsional motion leads to hyperfine patterns which
are qualitatively dependent on the torsional symmetry of the
levels.footnote{Coudert and Lopez, {em J.
Mol. Spectrosc.}~{bf 239} (2006) 135; and Tudorie,
Coudert, Huet, Jegouso, and Sedes, {em
J. Chem. Phys.}~{bf 134} (2011) 074314.} The interaction
between a large amplitude torsional motion and the hyperfine
coupling may also lead to a less known hyperfine effect,
the so-called magnetic spin-torsion coupling, which was
first studied by Heuvel and Dymanusfootnote{Heuvel and Dymanus, {em J. Mol. Spectrosc.}~{bf 45}
(1973) 282 and {em ibid} {bf 47} (1973) 363.} and which has
not yet been conclusively evidenced.
In this talk, the magnetic hyperfine structure of the non-rigid
methanol molecule will be investigated experimentally and
theoretically. 13 hyperfine patterns were recorded using two
molecular beam microwave spectrometers. These patterns, along
with previously recorded ones, were analyzed in an attempt
to evidence the effects of the magnetic spin-torsion coupling.
The theoretical approach setup to analyze the observed data
accounts for the spin-torsion coupling, in addition to the familiar
magnetic spin-rotation and spin-spin couplings, and relies
on symmetry considerations to build a hyperfine coupling
Hamiltonian and a spin-rotation-torsion wavefunction compatible
with the Pauli exclusion principle.
In the talk, the results of the analysis will be presented.
The hyperfine coupling parameters retrieved will be discussed
and we hope to be able to conclusively evidence the effects
of the magnetic spin-torsion.Made available in DSpace on 2016-01-05T20:05:01Z (GMT). No. of bitstreams: 3
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Letter from H. L. Russell to Carl Hayden
No full textLetter from H. L. Russell to Carl Hayden regarding fines in the park
Terahertz spectroscopy of deuterated acetaldehyde: CH2DCHO
No full textThis study follows our recent investigations about deuterated methyl-top species of complex organic molecules: methanol,\footnote{Coudert, L. H.; {\em et al.} {\em J. Chem. Phys.}~{\bf140}, (2014) 64307} methyl formate,\footnote{Coudert, L. H.; {\em et al.} {\em ApJ}~{\bf779}, (2013) 119} and dimethyl ether.\footnote{Richard, C.; {\em et al.} {\em A\&A}~{\bf552}, (2013) A117} In particular these works led the first ISM detection of \chem{HCOOCH_2D} and \chem{CH_2DOCH_3}.
Acetaldehyde is not very abundant in the ISM, but this is a very interesting case from the spectroscopic point of view as it is an intermediate case between methyl formate and methanol. In the normal species of acetaldehyde, the barrier to internal rotation\footnote{Smirnov, I. A.; {\em et al.} {\em J. Mol. Spectrosc.} ~{\bf295} (2014) 44} V is 408cm which is close to the value in methyl formate\footnote{Ilyushin, V.; {\em et al.} {\em J. Mol. Spectrosc.} ~{\bf255} (2009) 32}: 373 cm. However, the value of the Coriolis coupling constant is
0.33 in acetaldehyde which is a much larger value than in methyl formate,
0.08, meaning that the coupling between the torsion and the overall rotation
is more important. \\
The sample was not a commercial one and half of its amount is the normal
species which leads to a more difficult line assignment.
The spectra were recorded in Lille between 75 and 950~GHz with a solid-state
submillimeter-wave spectrometer. The starting point of the analysis was the centimeter-wave measurements carried out for the sym and asym- conformers.\footnote{Turner, P. H.; and Cox, A. P. {\em Chem. Phys. Lett.}~{\bf42}, (1976) 84 - Turner, P. H.; Cox, A. P.; and Hardy, J. A. {\em J.C.S. Farady Trans.}~{\bf2}, (1981) 1217}
A comparison between the approach developed for deuterated methyl formate
(\chem{HCOOCH_2D}), based on the water dimer formalism, and that designed
recently for deuterated methanol (\chem{CH_2DOH}) will be presented.\\
\em{This work is supported by the CNES and the Action sur Projets de l'INSU, PCMI.}Made available in DSpace on 2014-09-17T16:55:39Z (GMT). No. of bitstreams: 3
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HYPERFINE EFFECTS IN NON-RIGID MOLECULES WITH FIVE EQUIVALENT NUCLEI
No full text{A. A. Wolf, Q. Williams, and T. L. Weatherly, {\em J. Chem. Phys.{ R. L. Bhattacharjee, J. S. Muenter, and L. H. Coudert, {\em J. Chem. Phys.{{\em Soviet Maser Research,Author Institution: LISA, CNRS/Universites Paris 12 et 7, 61 Avenue du General de Gaulle, 94010 Creteil, FranceThe hyperfine structure of non-rigid molecules with five equivalent nuclei exchanged by one or several large amplitude motions has not yet been thoroughly investigated. This hyperfine structure should be of great interest for two reasons: {\em (i)} the form of the effective hyperfine coupling Hamiltonian to be used for the hyperfine energy level calculation depend on the nature of the tunneling sublevel being considered and {\em (ii)} hyperfine patterns depend on the symmetry species of the tunneling sublevels as a consequence of the Pauli principle. Such effects have already been studied in the case of non-rigid molecules with 3} {\bf 47,} 5101 (1967).} and 4} {\bf 97,} 8850 (1992).} equivalent nuclei, but not in the case of 5 equivalent nuclei. In all three cases, the hyperfine energy level calculation requires the so-called genealogical coefficients} Acad. D. V. Skobel'tsyn, Editor, New York, 1964.} which allow us to build symmetry-adapted nuclear spin wavefunctions characterized by a given value of the total nuclear spin angular momentum and by a given symmetry species of the group, which is the permutation group of identical particles. These coefficients are known for and 4, but not for . In this paper, the calculation of the genealogical coefficients for 5 identical nuclei will be carried out. They will be applied to the calculation of the hyperfine structure of non-rigid species with 5 identical nuclei such as PF, {\mbox{H}_5}^+, and {\mbox{D}_5}^+. For these species, the effective hyperfine coupling Hamiltonian will be derived and the genealogical coefficients will be used to diagonalize this Hamiltonian, to select the hyperfine energy levels obeying the Pauli principle, and to obtain hyperfine patterns
ANALYSIS OF THE LINE POSITIONS AND LINE INTENSITIES IN THE BAND OF THE WATER MOLECULE
No full textL. H. Coudert, J. Mol. Spectrosc. 165, 406 (1994). J.-M. Flaud, C. Camy-Peyret, and J. P. Maillard, Mol. Phys. 32, 499 (1976). C. Camy-Peyret, J.-M. Flaud, J. P. Maillard, and G. Guelachvili, Mol. Phys. 33, 1641 (1977). R. A. Toth, J. Opt. Soc. Am. B 11, 2236 (1991). Per Jensen, S. A. Tashkun, and Vl. G. Tyuterev, J. Mol. Spectrosc. 168, 271 (1994).Author Institution: Laboratoire de Physique Mol\'{e}culaire et Applications, C.N.R.S., Universit\'{e} Pierre et Marie CurieThe somewhat successful treatment developed to account for the anomalous centrifugal distortion displayed by the water has been slightly altered in order to permit a calculation of the rotational energy in the ground and in the vibrational states using the same set of spectroscopic constants. This new treatment has been used to carry out two analyses of large bodies of data relevant to the water molecule. In the first analysis, in addition to the rotational levels of the and vibrational states, infrared and microwave transitions within the ground and the vibrational states as well as infrared transitions belonging to the were considered. The unitless standard deviation of this first analysis is 1.4, the maximum - and a-values considered being 25 and 20, respectively, and 71 spectroscopic constants were used. In the second analysis, the intensities published by were included in a least squares fit procedure in which line-strengths were evaluated choosing a physically reasonable dipole moment function and computing its matrix elements with the spectroscopic constants of the first analysis. In the paper, the results obtained in the two analyses will be presented. The potential energy and dipole moment functions derived from the analyses will be discussed. The latter function will be compared to that obtained by other authors
Letter from Carl Hayden to L. H. Mcellherren
No full textLetter from Carl Hayden to L. H. McEllherren detailing the funeral of Hon. M. P. Kinkaid, Chairman of the Committee on Irrigation of Arid Lands as well as Hayden's travel plans for the summer
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