Chirped-pulse, FTMW spectroscopy of the lactic acid-H 2 O system Zbigniew Kisiel, a Ewa Białkowska-Jaworska, a Daniel P. Zaleski, b Justin L. Neill, b Amanda L.Steber, b Brooks H. Pate b a Institute of Physics, Polish Academy of Sciences, Warszawa, Poland c Department of Chemistry, University of Virginia, Charlottesville, Virginia, USA 66th OSU International Symposium on Molecular Spectroscopy WH10

Lactic acid primer: SsC (most stable conformer)  a = 1.44 D  b = 1.83 D GskC G’sk’C % AaT % Gauche matrix isolation ir + ab-initio,Borba,Gomez-Zavaglia,Lapinski,Fausto, less stable conformersPCCP 6, 2101 (2004) MMW of SsC Pszczolkowski et al., J.Mol.Spectrosc. 234, 106 (2005) ab-initio, LA+H 2 OSadlej et al., PCCP 8, 101 (2006) ab-initio, LA+nH 2 OSmaga,Sadlej, J.Phys.Chem.A 114,4427(2010) ir + ab-initio, LA aggregationLosada,Trang,Xu, J.Chem.Phys. 128, (2008)

Chirped-pulse Fourier transform microwave spectrometer with supersonic expansion: Developed in the Pate group, U of. Virginia, USA: Up to 10 GHz in a single shot ! Rev.Sci.Instrum. 79, (2008) Enhancements: - Several nozzles - Multiple chirps on one gas pulse

Analysis tools: AABS package + SPFIT/SPCAT: Line blanking

Chirped pulse spectrum of Lactic acid (+H 2 O): LA, SsC LA, AaT LA+H 2 O LA+(H 2 O) 2 (H 2 O) 2 Obs. Calc.

LA conformers observable in supersonic expansion: SsC  a = 1.49 D  b = 1.92 D AaT  a = 5.05 D  b = 0.60 D  E = +10.0kJ/mol  B3LYP/ G(d,p)

Relative intensities of SsC and AaT transitions: Obs. Calc ← ← ← MHz SsC AaT SsC AaT SsC AaT Calculation with:  a = 1.44 D for SsC  a = 5.05 D for AaT and AaT = 2% of SsC

AaT Constants for the lactic acid monomers: PC-GAMESS, B3LYP/ G(d,p) quartics  FCONV + VIBCA 20 a R-type lines 7 b R- and b Q-type  fit = 12.1 kHz SsC

Ab-initio predictions for LA + H 2 O: Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010) MP2/aug-cc-pVDZ Ia Ib Ic Most stable form with total binding energy kJ/mol

The J = 4 3 a R-type transition of LA+H 2 O: The J = 4  3 a R-type transition of LA+H 2 O: Obs. Calc. T=0.5K K a = MHz

Ab-initio predictions for LA+ 2 x H 2 O: Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010) IaIb IaIc dw-I In fact:

The J = 7 6 transition of LA+2H 2 O: The J = 7  6 transition of LA+2H 2 O: K a = Calc. T=1K a-type 7 07   6 06 b-type *

The J = 10 9 a R-type transition of LA+3H 2 O: The J = 10  9 a R-type transition of LA+3H 2 O: K a = Calc. T=1K

LA+3H 2 O LA+2H 2 O Constants for the lactic acid+water clusters: PC-GAMESS, MP2/aug-cc-pVDZ quartics  FCONV + VIBCA a R- and b R-type lines in all cases sometimes also b Q-types LA+H 2 O Large cycle

BSSE calculated binding energies (kJ/mol): body = 22% ≥ 3-body = 38%

Binding energies and H-bond lengths:  Å  Å  Å  Å  Å  Å

Comparison with water clusters:  Å  Å  Å  Å (H 2 O)  Å (H 2 O)  Å all at MP2/aug-cc-pVDZ

 The rotational spectrum of the less stable AaT conformer of lactic acid was assigned for the first time.  Supersonic expansion SsC : AaT ratio found to be close to the room temperature value.  Rotational spectra of LA + H 2 O, LA + 2H 2 O, LA + 3H 2 O assigned (either classically or using the “3-line” autofitting program (TC10, 65 th OSU Symposium).  The three clusters constitute a series of successively larger water chains bound in a cycle to the carboxylic group of the lactic acid.  The rotational constants, centrifugal distortion constants, and electric dipole moment components are in good semi-quantitative agreement with results of ab initio calculations. WH11  Attempts to observe the lactic acid dimers were eventually successful in that chemical dimers = lactides were identified in a heated sample (stay for the next talk = WH11 )SUMMARY: