The HITRAN 2008 molecular spectroscopic database

This paper describes the status of the 2008 edition of the HITRAN molecular spectroscopic database. The new edition is the first official public release since the 2004 edition, although a number of crucial updates had been made available online since 2004. The HITRAN compilation consists of several components that serve as input for radiative-transfer calculation codes: individual line parameters for the microwave through visible spectra of molecules in the gas phase; absorption cross-sections for molecules having dense spectral features, i.e. spectra in which the individual lines are not resolved; individual line parameters and absorption cross-sections for bands in the ultraviolet; refractive indices of aerosols, tables and files of general properties associated with the database; and database management software. The line-by-line portion of the database contains spectroscopic parameters for 42 molecules including many of their isotopologues.     

The Rotational-Torsional Spectrum of the g'Gg Conformer of Ethylene Glycol: Elucidation of an Unusual Tunneling Path

The microwave spectrum of the energetically unfavored g'Gg conformer of ethylene glycol (CH(2)OH&bond;CH(2)OH) is reported. This spectrum is dominated by an interconversion geared-type large-amplitude motion during which each OH group in turn forms the intramolecular hydrogen bond. The microwave spectrum has been analyzed with the help of a Watson-type Hamiltonian plus a 1.4-GHz tunneling splitting. The rotational dependence of this tunneling splitting has been examined using an IAM approach and this yielded qualitative information on the tunneling path the molecule uses to interconvert between its two most stable conformers. Unexpectedly, but in agreement with ab initio calculations, when tunneling occurs between the energetically equivalent g'Gg and gGg' conformers, the OH groups are rotated stepwise through 240 degrees in the sense of a flip-flop rather than a concerted rotation and the molecule goes through the more stable g'Ga and aGg' forms. The electronic reasons for preferring a long rather than a short rotational path via a gGg form are discussed using calculated adiabatic vibrational modes. Copyright 2001 Academic Press.     

Hyperfine coupling and large amplitude motions interaction in the water dimer

Experimental 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 ? 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.     

High-Lying Rotational Levels of Water: Comparison of Calculated and Experimental Energy Levels for (000) and (010) up to J = 25 and 21

Emission spectra of methane-oxygen low-pressure flames have been recorded at a resolution of 0.02 cm-1 with an infrared Fourier transform spectrometer in the spectral ranges 780-1370 and 1800-5000 cm-1. The flame temperature was about 1850 K and a large number of transitions involving J values as high as 34 for an extended set of vibrational states could be assigned. Combined with already published data sets on H2O, our line position analysis yielded rotational energy levels for many of these states, but only the results relevant to the ground and the (010) states are presented here. The experimental energies for these two states have been fitted with the help of the bending-rotation Hamiltonian approach [L. H. Coudert, J. Mol. Spectrosc. 181, 246-273 (1997)], and for each rotational level, the calculated energy along with its uncertainty is reported and compared with the observed value. Comparisons with other available energy level data sets for the ground and (010) states are also presented. Copyright 1999 Academic Press.     

High-speed stereoscopic PIV study of rotating instabilities in a radial vaneless diffuser

This paper presents an experimental analysis of the unsteady phenomena developing in a vaneless diffuser of a radial flow pump. Partial flow operating conditions were investigated using 2D/3C high repetition rate PIV, coupled with unsteady pressure transducers. Pressure measurements were acquired on the shroud wall of the vaneless diffuser and on the suction pipe of the pump, whereas PIV flow fields were determined on three different heights in the hub to shroud direction, inside the diffuser. The classical Fourier analysis was applied to both pressure signals to identify the spectral characteristics of the developing instabilities, and the high-order spectral analysis was exploited to investigate possible non-linear interaction mechanisms between different unsteady structures. A dedicated PIV averaging procedure was developed and applied to the PIV flow fields so as to capture and visualize the topology of the spectrally identified phenomena. The influence of these phenomena on the diffuser efficiency was also investigated.     

Unimer Exchange Is not Necessary for Morphological Transitions in Polymerization-Induced Self-Assembly

Polymerization-induced self-assembly (PISA) has established itself as a powerful and straightforward method to produce polymeric nano-objects of various morphologies in (aqueous) solution. Generally, spheres are formed in the early stages of polymerization that may evolve to higher order morphologies (worms or vesicles), as the solvophobic block grows during polymerization. Hitherto, the mechanisms involved in these morphological transitions during PISA are still not well understood. Combining a systematic study of a representative PISA system with rheological measurements, we demonstrate that—unexpectedly—unimer exchange is not necessary to form higher order morphologies during radical RAFT-mediated PISA. Instead, in the investigated aqueous PISA, the monomer present in the polymerization medium is responsible for the morphological transitions, even though it slows down unimer exchange.