1. 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

2. Lactic acid primer: SsC (most stable conformer)  a = 1.44 D  b = 1.83 D GskC +8.0kJ/mol3.6% @298K G’sk’C +8.62.9% AaT +10.01.6% 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, 014508 (2008)

3. 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, 053103 (2008) Enhancements: - Several nozzles - Multiple chirps on one gas pulse

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

5. 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.

6. 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  1.6% @298K B3LYP/6-311++G(d,p)

7. Relative intensities of SsC and AaT transitions: Obs. Calc. 2 12 ← 1 11 2 02 ← 1 01 2 11 ← 1 10 1 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

8. AaT Constants for the lactic acid monomers: PC-GAMESS, B3LYP/6-311++G(d,p) quartics  FCONV + VIBCA 20 a R-type lines 7 b R- and b Q-type  fit = 12.1 kHz SsC

9. Ab-initio predictions for LA + H 2 O: Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010) MP2/aug-cc-pVDZ Ia Ib Ic - 31.6 - 22.9 Most stable form with total binding energy - 40.9 kJ/mol

10. 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 = 1 0 2 2 1 1 MHz

11. Ab-initio predictions for LA+ 2 x H 2 O: Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010) IaIb IaIc dw-I - 71.8 - 64.4 - 66.0 In fact: - 87.8

12. The J = 7 6 transition of LA+2H 2 O: The J = 7  6 transition of LA+2H 2 O: K a = 1 0 2 5 4 4 3 3 2 1 Calc. T=1K a-type 7 07  6 16 7 17  6 06 b-type *

13. 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 = 1 0 2 6 55 3 4 4 1 3 2 Calc. T=1K

14. 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

15. BSSE calculated binding energies (kJ/mol): - 87.8 - 121.9 - 41.8 - 15.2 - 14.2 - 32.1 - 13.8 - 36.0 - 18.9 - 14.6 3-body = 22% ≥ 3-body = 38%

16. Binding energies and H-bond lengths: 2.621  Å 2.798  Å 2.652  Å 2.796  Å 2.710  Å 2.809  Å

17. Comparison with water clusters: 2.921  Å 2.710  Å 2.706  Å 2.720  Å (H 2 O) 3 2.803  Å (H 2 O) 4 2.748  Å all at MP2/aug-cc-pVDZ

18.  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: