Infrared spectra of the water-CO2 complex in the 4.3-3.6 micron region and determination of the ground state tunneling splitting for HDO-CO2

Spectra of water-CO2 dimers are studied using a tunable mid-infrared source to probe a pulsed slit jet supersonic expansion. H2O-CO2 and D2O-CO2 are observed in the CO2 nu3 fundamental region (~2350 cm-1), D2O-CO2 is also observed in the D2O nu3 fundamental region (~2790 cm-1), and HDO-CO2 is observed in the HDO O-D stretch fundamental region (~2720 cm-1), all for the first time in these regions. Analysis of the spectra yields excited state rotational parameters and vibrational shifts. They also yield the first experimental values of the ground state internal rotation tunneling splittings for D2O-CO2 (0.003 cm-1) and HDO-CO2 (0.0234 cm-1). The latter value is a direct determination made possible by the reduced symmetry of HDO-CO2. These results provide stringent and easily interpreted tests for theoretical water - CO2 potential energy surface calculations.Comment: 19 pages, 6 figure and 5 table

AB INITIO INVESTIGATION OF C2H2C_2H_2/X VAN DER WAALS COMPLEXES (X=NOBLE GAS, CO2CO_2, N2ON_2O)

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, BelgiumWe will present ab initio calculations performed at the MP2 and CCSD(T) levels of theory on acetylene containing complexes. We used large basis sets including or not midbond functions and corrected all results for the basis set superposition error. The influence of the monomer geometries on the properties of the complexes has been investigated. The topology of the intermolecular potential energy surfaces of the various complexes will be compared and the methodological approach adapted to the considered systems will be discussed

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

THE WEAKLY--BOUND CO2_2--ACETYLENE COMPLEX: FUNDAMENTAL AND TORSIONAL COMBINATION BAND IN THE CO2_2 ν3\nu_3 REGION

Author Institution: Laboratoire de Chimie quantique et Photophysique, CP160/09 Faculte des Sciences, Universite Libre de Bruxelles (U.L.B.), Ave. Roosevelt, 50 B-1050 Brussels, Belgium; Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N; 1N4, CanadaInfrared spectrum of the weakly-bound CO$_2$--C$_2$H$_2$ complex in the region of the CO$_2$ $\nu_3$ fundamental band ($\sim$ 2349 cm$^{-1}$) is observed in a pulsed supersonic slit jet expansion using a tunable diode laser probe. Two bands are observed and analyzed: the fundamental (C--O asymmetric stretch) and a combination involving the intermolecular torsional (out-of-plane bend) vibration. The resulting torsional frequency is 44.385(10) cm$^{-1}$. This represents the first observation of an intermolecular frequency for carbon dioxide-acetylene complex. A comparison between the results obtained here and those previously reported for N$_2$O--C$_2$H$_2$ complex is discussed

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

Structure and dynamics of the radical cation of ethane arising from the Jahn–Teller and pseudo-Jahn–Teller effects

The pulsed-field-ionization zero-kinetic-energy photoelectron spectrum of C2H6 has been recorded in the region of the adiabatic ionization threshold. The partially rotationally resolved spectrum indicates the existence of several vibronic states of C2H6+ with less than 600 cm−1 of internal excitation. The analysis of the rotational structures assisted by ab initio calculations enabled the determination of the adiabatic ionization energy of C2H6and the investigation of the structure and dynamics of C2H6+ at low energies. The ground state of C2H6+ is found to be a 2Ag state of diborane-like structure with strongly mixed (a1g)−1 and (eg)−1 configurations. The vibrational structure reveals the importance of large-amplitude nuclear motions involving the diborane distortion modes, the C–C stretching motion, and the internal rotation at elongated C–C distances. The spectrum is analyzed in the light of the information obtained in earlier studies of C2H6+ by ab initio quantum chemistry, EPR spectroscopy and photoelectron spectroscopy