Physique des Lasers, Atomes et Molécules UMR 8523 CNRS – Université Lille 1, 59655 Villeneuve d’Ascq Cedex, France 60th OSU International Symposium on Molecular Spectroscopy June 20-24, 2005 The urea-water complex observed by jet cooled Fourier-transform microwave spectroscopy and studied by ab initio calculations. J.-R. AVILES-MORENO, A. CUISSET, T. DELEPORTE, T.R. HUET, D. PETITPREZ.

Content Motivations: Urea: history and structure Urea-water complex Ab initio structure of the Urea-water complex Experimental set-up: MB-MWFTS Experimental spectrum: Lines with H2O Lines with D2O Determination of a first experimental structure Conclusions and outlook

Urea: history and structure (NH2)2C=O One of the Nature’s simplest biomolecule. A simplest diamide with 3 coordination sites. Important role in pharmaceutical chemistry Powerfull protein denaturing agent Anti-viral agent b a

Urea: history and structure (NH2)2C=O b a Conformer Plane C2v In the solid phase : planar a (C2v symmetry), intensive network of H-bonds In the gas phase : nonplanar and relatively floppy microwave spectra b ab initio calculations MP2 / 6-311++G(d,p) most stable conformer : anti form 1 Conformer Anti C2 2 Conformer Syn Cs b a a E/ kJ/mol 148 192 180 5 kJ/mol a (°) 2 1 a A S. Swaminathan et al, Acta Crystallogr., Sect B : struct. Sci. 40, 398, (1984) b P. D. Godfrey, R. D. Brown and A. N. Hunter, J. Mol. Struct. 413-414, 405, (1997)

UREA - WATER COMPLEX : motivation of the work b 1 Conformer H11 Anti Cs To study the micro-solvation process of bio-molecules : possible bridge between the gas phase and the liquid phase To understand the hydrogen bond formation. Possible comparison between physico-chemical data coming from experiment and ab initio calculations.

UREA - WATER COMPLEX : Ab initio structure Similar to formamide-water: F.J. Lovas et al J. Chem. Phys. 88(2) 722-729(1988) a b 1.85 Å 2.09 Å 1 3 0.7 3.6 130 180 230 2 Dihedral angle H11-O10-O2-C1 / ° E/ kJ/mol P.-O. Astrand, A. Wallqvist, G. Karlström, J. Chem. Phys. 100 (1994) 1262. Ab initio calculations at the B3LYP / aug-cc-pVTZ level of theory

Experimental set-up: MB-MWFTS Spectra recorded with a pulsed-nozzle MB-MWFTS in the 6-20 GHz frequency range. Optimization of the signal : T(K), carrier gas and pressure Heated nozzle T= 363-403 K Mirror Inside resonator Carrier gas P= 2-5 bar Carrier gas + H2O Urea powder H2O 40 mm Teflon

Experimental spectra Large survey scan in the 6-20 GHz frequency range with a mixture of : (14NH2)2 C=O + H2O (15NH2)2 C=O + H2O (14NH2)2 C=O + D2O (15NH2)2 C=O + D2O 4 strong lines around 12 GHz which can be identified as the Jka,kc=111-000 b-type transitions. Other lines around 17 GHz do not match with the urea-water complex (Jka,kc=212-101 transition for example).

Experimental spectra: Lines with H2O 14NH2CO14NH2– H2O 15NH2CO15NH2 – H2O 0.2 MHz 3.0 MHz 111 000 111000 ~ 300MHz 15NH2CO15NH2 111 000 14NH2CO14NH2 111000 Hyperfine structure Splitting ~ 300MHz T°C = 115 °C carrier gas : Ne at a total pressure of 3 bars Tests : with and without water ; different carrier gases (Ne, Ar, He)

Experimental spectra: Lines with D2O 0.2 MHz 3.0 MHz 14NH2CO14NH2– D2O 15NH2CO15NH2– D2O 111000 ~ 270 MHz MHz 14NH2CO14NH2– H2O 15NH2CO15NH2 – H2O 0.2 MHz 3.0 MHz 111 000 111000 ~ 300MHz T°C = 115 °C carrier gas : Ne at a total pressure of 3 bars Tests : with and without water ; different carrier gases (Ne, Ar, He)

Determination of a first experimental structure Calculation of the water molecule’s cartesian coordinates in the principal inertia axis of urea as a function of 2 internal coordinates (ρ and φ). Determination of the complex new inertia tensor, and diagonalisation. Calculations of the A, B and C rotational constants for each value of ρ and φ (-40° < ρ < 40° by step of 1° and -90° < φ < 90° by step of 1° ) Comparison between (A+C)calc and (A+C)obs

Determination of a first experimental structure H-bond length fixed to 1.9 Å a b ρ φ 2 internal rotations for H2O : ρ : around the 2O-5H axis φ : rotation of the 11H atom around the 9H-10O bond principal inertia axis of urea

Determination of a first experimental structure = | (A+C)calcd- (A+C)obsd | < 10 MHz for 47° < ρ <50° and 40°< φ <70° 14N14N - H2O φ (°) ρ (°) D (MHz)

Determination of a first experimental structure (A+C)calc (A+C)obs ρ = 47° φ = 55° 14N14N - H2O 12285 15N15N - H2O 11987 11977 ρ = 49° 14N14N - D2O 11770 11741 15N15N - D2O 11489 11475 r1=1.87Å r2=1.87Å =90°  * Fixed value

Conclusions and outlook First experimental observation of the urea-water complex. Searching for more urea-water complex lines. Possibility of a large amplitude motion of the H11 atom. Change of the H-bond length when going from H2O to D2O. In progress: analysis of the hyperfine structure

Experimental set-up: MB-MWFTS n  n0 t detection source polar gas e Molecules n0 n Source of microwave pulse (2-20 GHz) Matter-light interaction Inside a Pérot-Fabry resonator Polarization of the polar molecules ; Rotational cooling Detection and recording of the signal Emitted by the molecules As a function of time Fourier transform of the transient signal  Frequency analysis Application rule : maximum polarization for a p/2 pulse, i.e. Physical parameters : m : permanent electric dipole moment e : amplitude of the microwave field t : length of the microwave pulse

Experimental set-up: MB-MWFTS Gas mixture Vacuum-tight rotation transition and step by step motor Gaussian envelop (Ws= 42 mm at 12 GHz) MW pulse detection pump 600 mm<d< 650 mm R=800 mm Resonant cavity and pulsed supersonic beam Spectral range : 6 – 20 GHz Sensitivity : 10-11 cm-1 Resolution : 10 kHz Accuracy : 2.4 kHz Rot. temp. :  4 K Pressures : Carrier gas: 1-3 bars Molecules: 10-2 bar Secondary pumping Labview interface Scan : 1GHz/12h Heated nozzle 363 K Benzamide powder 1.5 bar Ar Carrier gaz Cavity

Transition rotationnelle Dédoublement Doppler Interrupteur rapide t Impulsion microonde de 1 à 2 ms Synthétiseur 2-20 GHz Cavité PF Amplificateur A/D FI = 30 MHz Mélangeur Filtre passe-bande Amplificateur RF Convertisseur A/D ns+30 MHz Transition rotationnelle Dédoublement Doppler