60th OSU International Symposium on Molecular Spectroscopy TF03 The millimeter-wave rotational spectrum of lactic acid Zbigniew Kisiel, Ewa Białkowska-Jaworska, Lech Pszczółkowski Institute of Physics, Polish Academy of Sciences Warszawa, Poland

The lactic acid molecule Borba et. al., PCCP 6, 2101 (2004)  ZPE  Population 298K SsC GskC G’sk’C AaT SsC GskC 16.4 kJ/mol

Lowest energy vibrational states in lactic acid  30 = 60 cm -1  28 = 240  29 = 224  27 = 287 vibrational spectrum: Borba et. al., PCCP 6, 2101 (2004) rotational spectrum: van Eijck, JMS 101, 133 (1983) Studied in this work, and assigned with confidence Measured, but only tentative assignment

The Warsaw broadband millimeter-wave spectrometer

The IFPAN MMW spectrometer GHz Istok BWO in electromagnet

Analysis carried out using the AABS software package All recorded spectra (typically 0.5 GHz each) combined into a single continuous spectrum Spectra and predictions displayed alongside with two previewing programs Graphical assignment and automated transfer of frequencies and quantum numbers to datafiles Fitting and predictions with ASFIT/ASROT (H.M.Pickett’s SPFIT/SPCAT can also be used) AABS = A ssignment and A nalysis of B roadband S pectra available on the PROSPE webpage:

Loomis-Wood type plot for K a = 1  0 transitions Ground state  30 = 1

 a /  b b: 32 8,24  31 9,23 a: 32 9,24  31 9,23 a: 32 8,24  31 8,23 b: 32 9,24  31 8,23  tot = 2.32 D  tot = 2.34 D  tot = 2.33 D

Spectroscopic constants determined for the ground state

Dataset for the ground state MMW: GHz FTMW: 8-16 GHz CMW: GHz

Quartic constants for the ground state GAMESSGAMESS FCONVFCONV VIBCAVIBCA } 1.2 %

The  30 satellite sequence ?? Sixth quantum ? 30 mode Observed for transitions with lowest values of K c, owing to the very small change in A on excitation of the 30 mode

Changes in constants on excitation of the 30 mode  quartics  octics sextics  A,B,C  KK JJ   C JJ

The 30 torsional mode Intramolecular hydrogen bond  30  60 cm - 1 GAMESSGAMESS output displayed with ChemCraftChemCraft

methyl torsion,  29 = 224 cm - 1 Assignment of the minor vibrational satellites

Lowest energy vibrational states in lactic acid  30 = 60 cm -1  28 = 240  29 = 224  27 = 287 v u ?

Conclusions:Conclusions: Spectroscopic constants determined for the ground state and nine different vibrational excited states Strongest features in rotational spectrum can be predicted with confidence well into the submillimeter-wave region Well-behaved rotational spectrum in lowest states: meaningful quartics in Watson’s Hamiltonian and all transitions fitted to within experimental accuracy Vibrational states crowded above 200 cm –1 and subject to various perturbations In progress: Dipole moment measurement Search for hydrogen-bonded complexes