DESCRIPTION OF THE FANTASIO INSTRUMENTAL SET-UP

Author Institution: Laboratoire de Chimie quantique et Photophysique, CP160/09, Universite Libre de Bruxelles (U.L.B.), Ave. F.-D. Roosevelt 50, Brussels, B-1050, BelgiumWe have built a new set-up, named $FANTASIO$, for "Fourier trANsform, Tunable diode and quadrupole mAss spectro\-meters interfaced to a Supersonic expansIOn". Initial results will be reported, including the mapping of the jet expansion and the observation of acetylene clusters in the infrared spectral range

The 2CH excitation band in C2H2-N2O and 2CH+torsion combination bands in C2H2-N2O and C2H2-CO2

A preliminary analysis of the 2CH excitation band in C2H2–N2O in the 1.5 mm range (K. Didriche, C. Lauzin, P. Macko, M. Herman and W.J. Lafferty, Chem. Phys. Letters 469, 35 (2009).), only considering 117 low J-, and Ka- vibration-rotation lines, is significantly extended thanks to the analysis of new spectra including very regular series of lines with J/Ka up to 31/15. 1271 b-type lines were assigned. Perturbations are briefly discussed. The rotational temperature in the experiments is estimated to be 20K and the upper state mean half-time is 1.6 ns for non perturbed levels. The previous analyses of the 2CH þ torsion band in C2H2–N2O and in C2H2–CO2 (C. Lauzin, K. Didriche, T. Fo¨ ldes and M. Herman, Mol. Phys. 109, 2105 (2011).), are also extended to include 286 and 234 lines, respectively, also correcting for calibration errors. New rotational constants are obtained using a rigid rotor Hamiltonian by simultaneously fitting the ground, 2CH and 2CH þ torsion states in C2H2–N2O, and the latter state, only, in C2H2–CO2

Torsional excitation in the 2CH vibrational overtone of the C2H2-CO2 and C2H2-N2O van der Waals complexes

Infrared spectra of the weakly-bound C 2H 2-CO 2 and C 2H 2-N 2O complexes in the region of the 2CH acetylene overtone band (∼1.52μm) were recorded using CW-cavity ring down spectroscopy in a continuous supersonic expansion. A new, c-type combination band is observed in each case. The rotational analysis of low J, K lines is performed and rotational constants are obtained. The band origins are 40.491(2) and 40.778(2) cm -1 higher in energy than the 2CH excitation bands for C 2H 2-CO 2 and C 2H 2-N 2O, respectively. The combination band is assigned in each case as involving intermolecular torsional excitation combined to 2CH. The values of the torsional vibrational frequency and of the x CH/torsion anharmonicity constant are briefly discussed. Copyright © 2011 Taylor and Francis Group, LLC

THE HIGH RESOLUTION SPECTRUM OF THE Ar−-C2_2H2_2 COMPLEX

Author Institution: Service de Chimie quantique et Photophysique; CP160/09, Faculte des Sciences, Universite Libre de Bruxelles (U.L.B.); Av. Roosevelt, 50, B-1050, Bruxelles, Belgium; LISA, CNRS/Universites Paris Est et Paris Diderot; 61 Avenue du General de Gaulle, 94010 Creteil, FranceNew spectra of the Ar$-$C$_2$H$_2$ van der Waals complex have been recorded using FANTASIO+, a new experimental setup with improved signal to noise and measurement accuracy~{\bf 108} (2010) 2155.} over the previous one, FANTASIO.~{\bf 113} (2009) 2359.} The spectra span the 6500--6600~cm$^{-1}$ region corresponding to the $\nu_1 + \nu_3$ band of isolated acetylene. Several bands of the complex were observed. The strongest one connects the two ground van der Waals states and could be rotationally assigned. The yet unassigned weaker bands are combination bands involving changes in the van der Waals modes quantum numbers. The new experimental data have first been used to refine an {\em ab initio} potential energy surface (PES) obtained at CCSD(T) level with large basis sets including bond functions. Combination differences involving rotational levels of the strongest band lower state were calculated up to $J=9$ and $K_a=1$ and fitted together with microwave~{\bf 72} (1980) 6020; and Liu and Jager, {\em J.~Molec.~Spec.}~{\bf 205} (2001) 177.} and infrared data. {\em J.~Chem.~Phys.}~{\bf 99} (1993) 8585; and Hu {\em et al.,} {\em J.~Molec.~Spec.}~{\bf 153} (1992) 486.} The approach used in the analysis treats exactly the large amplitude bending and stretching modes and the overall rotation of the complex. The parameters involved in the expansion~{\bf 123} (2005) 014309.} of the PES were fitted to the line positions yielding RMS values of 0.021~MHz and $0.6\times 10^{-3}$~cm$^{-1}$ for the microwave and infrared data, respectively. The new experimental data have also been used to refine the PES of the complex for the $v_1=v_3=1$ vibrational state of acetylene. Using the results of the previous analysis, rotational energies were retrieved for the strongest band upper state and analyzed. The results of this second analysis are not as satisfactory as the previous one. This may be due to perturbations or to the fact that the PES for the upper vibrational state differs from that of the ground vibrational state

Overtone (2NH) spectroscopy of NH3-Ar

The Π (11) ← Σ (00) 2NH (ν1+ν3) band of the NH3-Ar van der Waals complex formed in a supersonic jet expansion, with origin at 6628 cm -1 was recorded at high-resolution using cavity ring down spectroscopy. The analysis leads to upper state rotational constants and J-dependent predissociation lifetimes estimated from linewidth analysis, with a mean value about 0.6 ns.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Investigation of the C2 H2 - CO2 van der Waals complex in the overtone range using cw cavity ring-down spectroscopy

A slit nozzle supersonic expansion containing acetylene [492 SCCM (SCCM denotes cubic centimeter per minute at STP)] and carbon dioxide (740 SCCM) seeded into Ar (837 SCCM) is investigated using cw-cavity ring-down spectroscopy, in the 1.5 μm range. The C2 H2 - CO 2 van der Waals complex is observed around the v1 + v 3 acetylenic band. The rotational temperature is estimated to be close to 60 K from the comparison between observed and simulated spectra. The analysis of the main, perturbed B -type band centered near 6 549.280 cm -1, is performed. It is attributed to a dimer with the known planar, C2v geometry. The present overtone data, involving ground state levels with higher J/K states (J≤35 and Ka≤ 20) than previously reported, are combined to 3 μm data [D. G. Prichard, R. N. Nandi, J. S. Muenter, and B. J. Howard, J. Chem. Phys. 89, 1245 (1988); Z. S. Huang and R. E. Miller, Chem. Phys. 132, 185 (1989)] to determine improved ground state parameters. The major perturbations affecting the upper state are accounted for through C -type Coriolis resonances involving one dark state, whose symmetry must therefore be A1. Upper state constants are obtained for the bright and dark states. The dependence upon vibrational excitation is demonstrated to arise from excitation in the acetylene unit, only, for the former, but cannot be unravelled for the latter. © 2009 American Institute of Physics

FEMTO-FANTASIO: A VERSATILE EXPERIMENTAL SET-UP TO INVESTIGATE MOLECULAR COMPLEXES

Author Institution: Service de Chimie quantique et Photophysique CP160/09, Faculte des Sciences, Universite Libre de Bruxelles (U.L.B.), Av. Roosevelt, 50, B-1050, Bruxelles, BelgiumSeveral improvements have been made on the apparatus developed in Brussels for the study of jet-cooled molecules, named \hbox{FANTASIO nderline{\textbf{105}}(5-7), 815 (2007).} nderline{\textbf{463}}, 345 (2008).} nderline{\textbf{113}}, 2359 (2009).}}, for "Fourier trANsform, Tunable, diode and quadrupole mAss spectrometers interfaced to a Supersonic expansIOn". The upgraded setup, called Femto-FANTASIO, is presented.\\ These improvements include: a doubling of the pumping efficiency, by adding another turbomolecular pump Leybold MAG-W3200 CT; an increase in sensitivity in the 1.5 $\mu$m range thanks to a new CRDS system, consisting in new cavity mirrors, leading to a ring down time of 125 $\mu$s and a new detector, decreasing the noise level; a new injection system to probe samples liquid at STP conditions; a temperature controlled nozzle/slit; and as an alternative probe technique, an absorption source, tunable from 3000 to 9000 cm$^{-1}$, coupling an optical parametric oscillator (OPO), pumped by a Ti:Sa femtosecond laser, to a high resolution continuous scan Fourier transform interferometer.\\ Femto FANTASIO will be used to investigate molecular complexes. First results and achievements of this new setup are presented