High-Resolution Jet-Cooled Spectroscopy of SF6: The ν2+ ν6Combination Band of32SF6and the ν3Band of the Rare Isotopomers (original) (raw)
Related papers
Molecular Physics
Sulphur hexafluoride is a very strong greenhouse gas whose concentration is increasing in the atmosphere. It is detected through infrared absorption spectroscopy in the strong ν3 fundamental region. Due to the existence of low-lying vibrational states of this molecule, however, many hot bands arise at room temperature and those are still not known. We present here a contribution to the elucidation of this hot band structure, by analysing the ν2 + ν3 combination band. We use a supersonic jet expansion high-resolution spectrum at a rotational temperature of ca. 25 K that was recorded thanks to the Jet-AILES setup at the Source Optimisée de Lumière d’Energie Intermédiaire du LURE (SOLEIL) Synchrotron. The simplified structure of this cold spectrum allowed us to assign 444 rovibrational lines and to fit effective Hamiltonian parameters, leading to a very satisfactory spectrum simulation. The parameters obtained in this way allow to calculate the spectrum of the ν3+ν2−ν2 hot band.
Molecular Physics, 2014
The strong infrared absorption in the ν 3 S-F stretching region of sulphur hexafluoride (SF 6) near 948 cm −1 makes it a powerful greenhouse gas. Although its present concentration in the atmosphere is very low, it is increasing rapidly, due to industrial pollution. The ground state population of this heavy species is only 32% at room temperature and thus many hot bands are present. Consequently, a reliable remote-sensing spectroscopic detection and monitoring of this species require an accurate modelling of these hot bands. We used two experimental setups at the SOLEIL French synchrotron facility to record some difference and combination bands of SF 6 : (1) a new cryogenic multiple pass cell with 93 m optical path length and regulated at 163 ± 2 K temperature and (2) the Jet-AILES supersonic expansion setup. With this, we could obtain high-resolution absorption spectra of the ν 3 − ν 1 , ν 3 − ν 2 , ν 1 + ν 3 and ν 2 + ν 3 bands at low temperature. These spectra could be assigned and analysed, thanks to the SPVIEW and XTDS computer programs developed in Dijon. We performed two global fits of effective Hamiltonian parameters. The first one is a global fit of the ground state, ν 2 , ν 3 , ν 3 − ν 2 , ν 2 + ν 3 , 2ν 3 and 2ν 3 − ν 3 rovibrational parameters, using the present spectra and previous infrared, Raman and two-photon absorption data. This allows a consistent refinement of the effective Hamiltonian parameters for all the implied vibrational levels and a new simulation of the 2ν 3 + ν 2 − ν 2 hot band. The second global fit involves the present ν 3 − ν 1 and ν 1 + ν 3 lines, together with previous ν 1 Raman data, in order to obtain refined ν 1 parameters and also ν 1 + ν 3 parameters in a consistent way. This allows to simulate the ν 3 + ν 1 − ν 1 hot band.
Turkish journal of physics, 2012
Octahedral formalism based on the notions of molecular symmetry is used in the calculation of the position lines of the ϑ4 band of 34 SF 6 ; we used an experimental spectrum near 650 cm −1 .T his spectrum was analysed using XTDS and SPVIEW software’s, developed in Dijon, France. We have 37 parameters to determined at the six order and for Jmax = 95, using 1497 data. We have obtained an RMS =0 .598 × 10 −3 cm −1 .
Synchrotron radiation induced fluorescence spectroscopy of SF6
Journal of Physics B: Atomic, Molecular and Optical Physics, 2005
This thesis summarizes my research on gas phase molecules in the VUV and soft Xray energy range by means of synchrotron radiation induced UV-Vis-nearIR fluorescence spectroscopy at the Section of Atomic and Molecular Physics, KTH. The novel contributions are outlined below: A new experimental setup for gas phase fluorescence studies using synchrotron radiation has been designed and constructed to perform simultaneously total and dispersed fluorescence measurements. Neutral photodissociation of CO has been investigated after excitation with 19-26 eV photons. Fluorescence from 3p 3 P, 3p 3 S and 3p 1 D excited states in carbon was recorded and interpreted by ab initio calculations. The population and dissociation of states belonging to the C and D Rydberg series in CO seem to explain the production of the observed triplet states but not the 3p 1 D state. Neutral photodissociation of NO is reported in the 17-26 eV energy range. No known molecular states can account for the collected data. New information regarding the precursor states of the observed neutral dissociation is provided by ab initio calculations. Autoionization of superexcited states in molecular nitrogen is evidenced by strong deviations of the Franck-Condon ratio in the fluorescence of the N 2 + B state. Ab initio calculations predict the existence of autoionizing-excited states that may account for some of the observed structures in the 20-46 eV energy range. Selective molecular fluorescence from the npσ 1 Σ u + and npπ 1 Π u (n=3-7) Rydberg levels to the E,F 1 Σ g + state in H 2 was recorded and rotationally analyzed. Vibrational levels of the E,F 1 Σ g + state (v EF =0,1,3,6-10) are determined. The predissociation of npπ 1 Π + levels is observed in agreement with the literature. Fragmentation of SF 6 was investigated after excitation with 25-80 eV photons. Dispersed fluorescence measurements reveal the emission of S, S + , F and F + excited atoms. These fragments are produced after single, double and triple excitations as well as direct ionizations and shake-ups in SF 6. Photoabsorption and fluorescence yield have been measured in SF 5 CF 3 using 10-30eV photons. The photoabsorption spectrum can be explained in terms of its similarities to those of the SF 6 and CF 4 molecules. The dispersed and un-dispersed fluorescence resemble those of the CF 3 X family. Several features suggest the migration of an F atom across the S-C bond that fragments the molecule producing excited CF 4. Doubly excited states of H 2 have been investigated in the range of 26-60 eV by monitoring Balmer α emission. The experimental data show the already known emission correlated with the fragmentation of the Q 1 and Q 2 states, and new features which could be attributed to dissociative photoionization and higher lying doubly excited states Q n (n>2) of the hydrogen molecule.
Nitrogen-Broadening Parameters for Atmospheric Spectra Modelling of the ν3 Band of SF6
Molecules, 2022
The infrared absorption of the ν3 band region of SF6, at temperatures spanning the 130 to 297 K range, has been reexamined using improved instrumentation with one goal: to estimate the broadening of parameters by nitrogen gas. These parameters are compared to previous literature predictions and an extended set of IR cross-sections is proposed and compared to other existing datasets.
High-resolution FTIR spectrum and analysis of the ν2+ν4 combination band of 32SF6
Journal of Molecular Spectroscopy, 2003
The spectroscopic knowledge of sulfur hexafluoride, which is necessary for a correct remote sensing and monitoring of this species in the EarthÕs atmosphere, is still very partial. In particular, the hot bands in the strongly absorbing m 3 region (near 948 cm À1) have not been analyzed yet. Their study implies the analysis of many vibrational levels and thus the spectroscopy of various fundamental, harmonic, and combination bands. The present work is a new contribution to this topic, concerning the m 2 þ m 4 combination band. The FTIR spectrum of this region has been recorded at room temperature with a resolution of 0.002 cm À1. The data have been analyzed thanks to the HTDS software (http://www.u-bourgogne.fr/LPUB/shTDS.html) developed in Dijon for XY 6 octahedral molecules. Seven hundred and fifty-nine lines could be assigned up to J ¼ 112, and the standard deviation is 0.0022 cm À1. The distance between the two vibrational sublevels with respective symmetry F 1u and F 2u is 0.348 cm À1 .
Journal of Molecular Spectroscopy, 2000
An extended set of 321 frequencies of vibration-rotation lines of the 3 band of SF 6 has been measured by saturation spectroscopy using various isotopic species of CO 2 . A least-squares fit of these data has been performed using an effective Hamiltonian written either with a spherical tensor or with a cubic tensor formalism. We have derived correspondence formulas between the parameters in the two approaches and checked that both formalisms give the same results up to the seventh order. Corrected parameters are given for the fit with a fifth-order Hamiltonian. An accurate representation of the band is obtained at the tenth order (standard deviation Ϸ 12 kHz) with a remarkable predictive power (better than 40 kHz) for J values Յ 100. The convergence properties of the Hamiltonian power expansion are discussed.
Structure and IR‐spectrum calculations for small SF6 clusters
The Journal of Chemical Physics, 1995
A new second order perturbation approach for evaluating the splittings and shifts of the vibrational bands of homogeneous molecular clusters, consistently treating degenerate normal modes, is described. The Hamiltonian of the system comprises harmonic and anharmonic intramolecular vibration terms, and the intermolecular potential. The anharmonic intramolecular contributions and the intermolecular potential are treated as a perturbation. A new site-site intermolecular potential model for SF 6 , featuring exchange, dispersion, electrostatic and induction terms, is presented. The new potential, with the parameters adjusted according to the observed monomer transition dipole moment and reproducing the experimental temperature dependence of the second virial coefficient, is used to determine SF 6 cluster structures up to the hexamer and, by means of the new line shift formalism, to calculate the corresponding IR-spectra in the region of the 3 vibrational mode ͑at 947.968 cm Ϫ1). The contributions of the various potential terms to the frequency shifts are analyzed and the leading interaction mechanism is confirmed to be the electrostatic one ͑implicitly the resonant dipole-dipole coupling͒. The theoretical spectra are shown to fairly describe the experimental evidence when considering only exchange, dispersion and electrostatic interactions. With the available atomic polarizabilities, induction seems to lead to a systematic redshift of the entire spectrum for all cluster sizes. The structure of the cluster vibrations is investigated in terms of the individual monomer vibrations and is correlated with the found geometrical cluster configurations.