Marcel Snels

Spectroscopic evidence for NAT, STS, and ice in MIPAS infrared limb emission measurements of polar stratospheric clouds

Spectroscopic evidence for β-NAT, STS, and ice in MIPAS infrared limb emission measurements of polar stratospheric clouds M. Höpfner, B. P. Luo, P. Massoli, F. Cairo, R. Spang, M. Snels, G. Di Donfrancesco, G. Stiller, T. von Clarmann, H. Fischer, and U. Biermann Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung, Karlsruhe, Germany Institut für Atmosphäre und Klima, ETH-Hönggerberg, Zürich, Switzerland Consiglio Nazionale delle Ricerche, Istituto di Scienze dell’Atmosfera e del Clima, Rome, Italy Forschungszentrum Jülich, Institut für Chemie und Dynamik der Geosphäre, Jülich, Germany Ente per le Nuove tecnologie, l’Energie e l’Ambiente, Rome, Italy Max-Planck-Institut für Chemie, Abteilung Atmosphärenchemie, Mainz, Germany now at: Referat für Umweltund Energiepolitik des SPD-Parteivorstandes, Berlin, Germany

The NH and ND stretching fundamentals of 14ND2H

High resolution (0.004 cm−1 instrumental bandwidth) interferometric Fourier transform infrared spectra of 14ND2H were obtained on a BOMEM DA002 spectrometer under essentially Doppler limited conditions. We report the analysis of the ND and NH stretching fundamentals of 14ND2H with term values for the symmetric (s) and antisymmetric (a) sublevels with respect to the inversion plane of the planar geometry Tv (s)=2430.7990(7) cm−1 and Tv (a)=2434.6222(8) cm−1 for the ν3a fundamental, Tv (s)=2559.8069(8) cm−1 and Tv (a)=2559.9630(9) cm−1 for the ν3b fundamental and Tv (s)=3404.238(5) cm−1 and Tv (a)=3404.316(5) cm−1 for the ν1 fundamental. The two modes ν3 which are degenerate in ND3 and whose degeneracy is lifted in ND2H, are distinguished by the subscripts 3a or 3b, being symmetric (3a) or antisymmetric (3b) with respect to the Cs plane of symmetry of the equilibrium geometry of ND2H. Up to 20 molecular parameters of the effective S-reduced Hamiltonian could be determined accurately for each fundamental. In...

Mode selective tunneling dynamics observed by high resolution spectroscopy of the bending fundamentals of N14H2D and N14D2H

High resolution (0.004 and 0.01 cm(-1) instrumental bandwidth) interferometric Fourier transform infrared spectra of (14)NH2D and (14)ND2H were measured on a Bomem DA002 spectrometer in a supersonic jet expansion and at room temperature. We report the analysis of the bending fundamentals of (14)NH2D with term values Tv(s)=1389.9063(2) cm(-1) and Tv(a)=1390.4953(2) cm(-1) for the nu(4b) fundamental and Tv(s)=1605.6404(7) cm(-1) and Tv(a)=1591.0019(7) cm(-1) for the nu(4a) fundamental, and of (14)ND2H with term values of Tv(s)=1233.3740(2) cm(-1) and Tv(a)=1235.8904(2) cm(-1) for the nu(4a) fundamental and Tv(s)=1461.7941(9) cm(-1) and Tv(a)=1461.9918(19) cm(-1) for the nu(4b) fundamental. In all cases Tv(s) gives the position of the symmetric inversion sublevel (with positive parity) and Tv(a) the position of the antisymmetric inversion sublevel (with negative parity). The notation for the fundamentals nu(4a) and nu(4b) is chosen by correlation with the degenerate nu(4) mode in the C(3v) symmetric molecules NH3 and ND3. The degeneracy is lifted in Cs symmetry and a indicates the symmetric, b the antisymmetric normal mode with respect to the Cs symmetry plane in NH2D and ND2H. Assignments were established with certainty by means of ground state combination differences. About 20 molecular parameters of the effective S-reduced Hamiltonian could be determined accurately for each fundamental. In particular, the effect of Fermi resonances of the 2nu(2) overtone with the nu(4a) bending mode was observed, leading to an increased inversion splitting in the case of ND2H and to a strongly increased inversion splitting and an inverted order of the two inversion levels in NH2D. Rotational perturbations observed with the nu(4b) bending fundamentals are probably due to Coriolis interactions with the inversion overtone 2nu(2). The results are important for understanding isotope effects on the inversion in ammonia as well as its selective catalysis and inhibition by excitation of different vibrational modes, as treated by quantum dynamics on high dimensional potential hypersurfaces of this molecule.

The v 1 and v 3 bands of ND3

High resolution (0.004cm-1 instrumental bandwidth) interferometric Fourier transform infrared spectra of 14ND3 were obtained on a BOMEM DA002 spectrometer under essentially Doppler limited conditions. An analysis is reported of the ND3 stretching fundamentals with band centres at [EQUATION]1 0 (s ← a) = (2420.056 ± 0.001)cm−1, [EQUATION]1 0(a ← s) = (2420.650 ± 0.001)cm−1, [EQUATION]3 0(a ← a) = (2563.8840 ± 0:0005)cm−1 and [EQUATION]3 0 (s ← s) = (2563.9161 ± 0.0005)cm−1, with inversion tunnelling splittings Δ[EQUATION]1 = 0.5412cm−1 and Δ[EQUATION]3 = 0.0209cm−1 in the vibrationally excited levels. About 50 parameters of the effective Hamiltonian for this band system could be determined accurately. Assignments were established with certainty by means of ground state combination differences. The results are important for and are discussed in relation to the mode selective inhibition and promotion of inversion at the nitrogen atom by exciting ND stretching vibrations, and treatments of isotope e? ects on inversion of ammonia by means of effective Hamiltonians and true molecular Hamiltonians on high dimensional potential hypersurfaces.

Rotational analysis of the ν1 band of trichlorofluoromethane from high resolution Fourier transform and diode laser spectra of supersonic jets and isotopically enriched samples

The spectrum of CCl3F (trichlorofluoromethane, CFC 11) has been measured in the region of the ν1 fundamental (1050–1120 cm−1) by high resolution interferometric Fourier‐transform spectroscopy [0.004 cm−1 bandwidth full width at half maximum, apodized] and by diode laser spectroscopy (bandwidth 0.0008–0.0020 cm−1 FWHM) at room temperature, in cold cells and in supersonic jet expansions. Fourier‐transform infrared and diode laser spectra of isotopically pure C35Cl3F have been recorded at room temperature in static cells. The C35Cl3F spectra allowed an analysis of the rotational structure to be started successfully for the first time. The rotational analysis of the isotopic species C35Cl237ClF and C35Cl37Cl2F, which are asymmetric rotors, was initiated from diode laser spectra of natural CCl3F with a rotational temperature of about 20 K (5% seeded in He) resulting from expansion in a supersonic pulsed slit jet. The rotational analysis yielded effective Hamiltonian constants including accurate band centers fo...

High resolution Fourier‐transform infrared spectroscopy of CHCl2F in supersonic jets: Analysis of ν3, ν7, and ν8

The spectrum of CHCl2F (fluorodichloromethane, CFC 21) has been measured in the region of the ν3, ν7, and ν8 fundamentals (700–1300 cm−1, including the atmospheric window) by high resolution interferometric Fourier‐transform spectroscopy [0.004 cm−1 bandwidth apodized, full width at half‐maximum (FWHM)] in supersonic jet expansions with a rotational temperature of ∼70 K and at room temperature in static cells. The supersonic jet spectra allowed an analysis of the rotational fine structure to be started successfully and carried on to the room temperature spectra. Effective Hamiltonian constants have been obtained with accurate band centers for the two most abundant isotopes CH35Cl2F(CH35Cl37ClF), ν8=807.1749(805.0492) cm−1, ν3=1079.4276(1079.3893) cm−1, and ν7=1239.1940(1238.6884) cm−1. Excited state rotational constants and improved ground state rotational constants including quartic centrifugal distortion in the Watson Hamiltonian are reported as well as hot bands and further bands in anharmonic reson...

Estimate of the Arctic Convective Boundary Layer Height from Lidar Observations: A Case Study

A new automated small size lidar system (microlidar or MULID) has been developed and employed to perform aerosol measurements since March 2010 at Ny Alesund (, ), Svalbard. The lidar observations have been used to estimate the PBL height by using the gradient method based on abrupt changes in the vertical aerosol profile and monitor its temporal evolution. The scope of the present study is to compare several approaches to estimate the PBL height, by using lidar observations, meteorological measurements by radio soundings, and a zero-order one-dimensional model based on a parameterization of the turbulent kinetic energy budget within the mixing layer, under the assumptions of horizontal homogeneity, and neglecting radiation and latent heat effects. A case study is presented here for a convective PBL, observed in June 2010 in order to verify whether the Gradient Method can be applied to lidar measurements in the Arctic region to obtain the PBL height. The results obtained are in good agreement with the PBL height estimated by the analysis of thermodynamic measurements obtained from radio sounding and with the model.

Excited vibrational states of benzene: High resolution FTIR spectra and analysis of some out-of-plane vibrational fundamentals of C6H5D

Abstract We have measured the infrared spectra of the ν 4 , ν 10b and ν 11 fundamental bands of C 6 H 5 D in the range 540–830 cm −1 with an instrumental bandwidth of 0.0024 cm −1 (unapodized FWHM) using a Bomem DA 002 Interferometric Fourier Transform spectrometer. The rotational analysis for ν 4 yields ground state constants by combining ground state combination differences and published microwave data (M. Oldani and A. Bauder, Chem. Phys. Lett. 108 (1984) 7). Excited state constants for the ν 4 level were obtained up to quartic terms, using Watsons A-reduction Hamiltonian in the III r representation, resulting in a band center ν 4 0 =697.593 cm −1 . A partial analysis is presented for the ν 10b fundamental ( ν 10b 0 =778.027 cm −1 ), which appears to be locally perturbed by the ν 16a + ν 16b combination band. The very strong ν 11 band is strongly perturbed, most probably by ν 6a and ν 6b . The results are discussed in relation to comparison with accurate ab initio electronic structure calculations including non Born-Oppenheimer effects as well as potential applications with isotope tracer detection and infrared laser chemistry.

High-resolution Fourier-transform infrared spectroscopy of the v 3(F2) fundamental of RuO4

The v 3(F2) fundamental band of ruthenium tetroxide (RuO4) vapour is investigated by high-resolution (0·004 cm-1 FWHM) interferometric FTIR spectroscopy in the range 850–1000 cm-1. The rotational fine structure is largely resolved and accurately analysed on the basis of third- and fourth-order (diagonal) effective Hamiltonians in the theory of Moret-Bailly. The analysis of the enriched isotopomer spectra gives m = 921·6514 cm-1 (102RuO4) and m = 920·0674 cm-1 (104RuO4). Many other constants for these are summarized in tables. For other isotopomers we find m(96) = 926‥d83 cm-1, m (99) = 924·14 cm-1, m(100) = 923·31 cm-1 and m(101) = 922·46 cm-1 from an approximate analysis of the spectrum of the natural isotope mixture. Many coincidences of rovibrational transitions in RuO4 with N2O and CO2 laser lines are predicted and assigned. The importance of the results for sub-Doppler spectroscopy, IR-laser isotope separation and the analysis of symmetry (and parity) selection rules is discussed briefly.

Calibration method for depolarization lidar measurements

A new method has been developed for calibration of the depolarization measurement of an atmospheric lidar. The technique requires a simple polarizer, and can be performed without interfering with the measurement set-up. The theoretical background of the procedure will be given and results of this calibration procedure on the tropospheric stratospheric aerosol lidar in McMurdo will be presented.