899 research outputs found
An ab initio HCN and HNC rotational vibrationallinelist for astronomy
We present a new ab initio HCN/HNC linelist. The linelist forms themost accurate and extensive HCN/HNC data set presently in existence.The data contain rotation vibration line frequencies and line strengths,for all transitions that are not rigorously dipole forbidden, between stateswith energy less than 18 000 cm-1 and with J ? 60
Opacity data for HCN and HNC from a new ab initio line list
A new extensive ab initio rotation-vibration HCN/HNC line list is presented. The line list contains rotation-vibration energy levels, line frequencies, and line strengths for transitions between states with energy less than 18,000 cm-1 and with Jâ¤60. This line list greatly improves the quality and range of HCN/HNC data available. It is presently the most extensive and most accurate ab initio HCN/HNC line list in existence. It is hoped that this data set will be used in models of C star atmospheres and elsewhere
Spectroscopically determined potential energy surface of H216O up to 25 000 cmâ1
A potential energy surface for the major isotopomer of water is constructed by fitting to observed vibrationârotation energy levels of the system using the exact kinetic energy operator nuclear motion program DVR3D. The starting point for the fit is the ab initio BornâOppenheimer surface of Partridge and Schwenke [J. Chem. Phys. 106, 4618 (1997)] and corrections to it: both one- and two-electron relativistic effects, a correction to the height of the barrier to linearity, allowance for the Lamb shift and the inclusion of both adiabatic and nonadiabatic non-BornâOppenheimer corrections. Fits are made by scaling the starting potential by a morphing function, the parameters of which are optimized. Two fitted potentials are presented which only differ significantly in their treatment of rotational nonadiabatic effects. Energy levels up to 25 468 cmâ1 with J = 0, 2, and 5 are fitted with only 20 parameters. The resulting potentials predict experimentally known levels with Jâ¤10 with a standard deviation of 0.1 cmâ1, and are only slightly worse for J = 20, for which rotational nonadiabatic effects are significant. The fits showed that around 100 known energy levels are probably the result of misassignments. Analysis of misassigned levels above 20 000 cmâ1 leads to the reassignment of 23 transitions
Experimental energy levels of the water molecule
Experimentally derived energy levels are presented for 12 248 vibrationârotation states of the H2 16O isotopomer of water, more than doubling the number in previous, disparate, compilations. For each level an error and reference to source data is given. The levels have been checked using energy levels derived from sophisticated variational calculations. These levels span 107 vibrational states including members of all polyads up to and including 8v. Band origins, in some cases estimates, are presented for 101 vibrational modes
Emission spectrum of hot HDO in the 380-2190 cm(-1) region
Fourier transform emission spectra were recorded using a mixture of H2O and D2O at a temperature of 1500 degreesC. The spectra were recorded in three overlapping sections and cover the wavenumber range 380-2190 cm(-1). A total of 22106 lines were measured, of which 60% are thought to belong to HDO. A total of 6430 FIDO transition,, are assigned, including the first transitions to the (040) vibrational state, with a term value of 5420.042 cm(-1). A total of 1536 new energy levels of HDO belonging to the (000), (010) (020), (030), and (040) stated are presented, significantly extending the degree of rotational excitation compared to previous studies. (C) 2001 Elsevier Science
Beyond the Born-Oppenheimer approximation: high-resolution overtone spectroscopy of H2D+ and D2H+
Transitions to overtone 2v2 and 2v3, and combination v2 + v3 vibrations in jet-cooled H2D+ and D2H+ molecular ions have been measured for the first time by high-resolution IR spectroscopy. The source of these ions is a pulsed slit jet supersonic discharge, which allows for efficient generation, rotational cooling, and high frequency (100 KHz) concentration modulation for detection via sensitive lock-in detection methods. Isotopic substitution and high-resolution overtone spectroscopy in this fundamental molecular ion permit a systematic, first principles investigation of BornâOppenheimer "breakdown" effects due to large amplitude vibrational motion as well as provide rigorous tests of approximate theoretical methods beyond the BornâOppenheimer level. The observed overtone transitions are in remarkably good agreement (<0.1 cmâ1) with non-BornâOppenheimer ab initio theoretical predictions, with small but systematic deviations for 2v2, 2v + 3v, and 2v3 excited states indicating directions for further improvement in such treatments. Spectroscopic assignment and analysis of the isotopomeric transitions reveals strong Coriolis mixing between near resonant 2v3 and 2v + 3v vibrations in D2H+. Population-independent line intensity ratios for transitions from common lower states indicate excellent overall agreement with theoretical predictions for D2H+, but with statistically significant discrepancies noted for H2D+. Finally, H2D+ versus D2H+ isotopomer populations are analyzed as a function of D2/H2 mixing ratio and can be well described by steady state kinetics in the slit discharge expansion
QED correction for H
A quantum electrodynamics (QED) correction surface for the simplest
polyatomic and polyelectronic system H is computed using an approximate
procedure. This surface is used to calculate the shifts to vibration-rotation
energy levels due to QED; such shifts have a magnitude of up to 0.25 cm
for vibrational levels up to 15~000 cm and are expected to have an
accuracy of about 0.02 cm. Combining the new H QED correction
surface with existing highly accurate Born-Oppenheimer (BO), relativistic and
adiabatic components suggests that deviations of the resulting {\it ab initio}
energy levels from observed ones are largely due to non-adiabatic effects
ExoMol line lists - III. An improved hot rotation-vibration line list for HCN and HNC
A revised rotation-vibration line list for the combined hydrogen cyanide (HCN)/hydrogen isocyanide (HNC) system is presented. The line list uses ab initio transition intensities calculated previously and extensive data sets of recently measured experimental energy levels. The resulting line list has significantly more accurate wavelengths than previous ones for these systems. An improved value for the separation between HCN and HNC is adopted, leading to an approximately 25 per cent lower predicted thermal population of HNC as a function of temperature in the key 2000 to 3000âK region. Temperature-dependent partition functions and equilibrium constants are presented. The line lists are validated by comparison with laboratory spectra and are presented in full as supplementary data to the article and at www.exomol.com
High accuracy calculations of the rotation-vibration spectrum of H
Calculation of the rotation-vibration spectrum of H3+, as well as of its
deuterated isotopologues, with near-spectroscopic accuracy requires the
development of sophisticated theoretical models, methods, and codes. The
present paper reviews the state-of-the-art in these fields. Computation of
rovibrational states on a given potential energy surface (PES) has now become
standard for triatomic molecules, at least up to intermediate energies, due to
developments achieved by the present authors and others. However, highly
accurate Born--Oppenheimer energies leading to highly accurate PESs are not
accessible even for this two-electron system using conventional electronic
structure procedures e.g., configuration-interaction or coupled-cluster
techniques with extrapolation to the complete basis set limit). For this
purpose highly specialized techniques must be used, e.g., those employing
explicitly correlated Gaussians and nonlinear parameter optimizations. It has
also become evident that a very dense grid of \ai\ points is required to obtain
reliable representations of the computed points extending from the minimum to
the asymptotic limits. Furthermore, adiabatic, relativistic, and QED correction
terms need to be considered to achieve near-spectroscopic accuracy during
calculation of the rotation-vibration spectrum of H3+. The remaining and most
intractable problem is then the treatment of the effects of non-adiabatic
coupling on the rovibrational energies, which, in the worst cases, may lead to
corrections on the order of several \cm. A promising way of handling this
difficulty is the further development of effective, motion- or even
coordinate-dependent, masses and mass surfaces. Finally, the unresolved
challenge of how to describe and elucidate the experimental pre-dissociation
spectra of H and its isotopologues is discussed.Comment: Topical review to be published in J Phys B: At Mol Opt Phy
Paper Session III-B - Local Space Service: A New Step in the Earth Observation
This paper Is to present a new Russian space project of the Earth Monitoring - Local Space Service (LOCSS), being developed by the Association for the Advancement of Space Science and Technology in cooperation with a number of leading space companies and agencies
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