Transcript law.pptx

66th OSU International Symposium on Molecular Spectroscopy
WH10
Chirped-pulse, FTMW spectroscopy of
the lactic acid-H2O system
Zbigniew Kisiel,a Ewa Białkowska-Jaworska,a
Daniel P. Zaleski,b Justin L. Neill,b
Amanda L.Steber,b Brooks H. Pate b
aInstitute
of Physics, Polish Academy of Sciences,
Warszawa, Poland
cDepartment
of Chemistry, University of Virginia,
Charlottesville, Virginia, USA
Lactic acid primer:
SsC (most stable conformer) a = 1.44 D
b = 1.83 D
GskC
G’sk’C
AaT
+8.0kJ/mol 3.6% @298K
+8.6
+10.0
2.9%
1.6%
Gauche
matrix isolation ir + ab-initio,
less stable conformers
Borba,Gomez-Zavaglia,Lapinski,Fausto,
PCCP 6, 2101 (2004)
MMW of SsC
Pszczolkowski et al., J.Mol.Spectrosc. 234, 106
(2005)
ab-initio, LA+H2O
ab-initio, LA+nH2O
Sadlej et al., PCCP 8, 101 (2006)
Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010)
ir + ab-initio, LA aggregation
Losada,Trang,Xu, J.Chem.Phys. 128, 014508
(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 !
Enhancements:
- Several nozzles
- Multiple chirps on
one gas pulse
• Rev.Sci.Instrum. 79,
053103 (2008)
Analysis tools: AABS package + SPFIT/SPCAT:
Line blanking
Chirped pulse spectrum of Lactic acid (+H2O):
(H2O)2
Obs.
LA, SsC
LA, AaT
Calc.
LA+(H2O)2
LA+H2O
LA conformers observable in supersonic expansion:
SsC a = 1.49 D
b = 1.92 D
AaT a = 5.05 D
b = 0.60 D
DE = +10.0 kJ/mol
B3LYP/6-311++G(d,p)
 1.6% @298K
Relative intensities of SsC and AaT transitions:
212 ← 111
SsC
AaT
202 ← 101
SsC
AaT
211 ← 110
SsC
AaT
Obs.
Calc.
1 MHz
Calculation with:
and AaT = 2% of SsC
a = 1.44 D for SsC
a = 5.05 D for AaT
Constants for the lactic acid monomers:
SsC
PC-GAMESS, B3LYP/6-311++G(d,p)
quartics  FCONV + VIBCA
AaT
20 aR-type lines
7 bR- and bQ-type
sfit = 12.1 kHz
Ab-initio predictions for LA + H2O:
Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010)
MP2/aug-cc-pVDZ
Ia
Ib
- 31.6
Ic
Most stable form with
total binding energy
- 40.9 kJ/mol
- 22.9
The J = 4  3 aR-type transition of LA+H2O:
Ka =
1
0
Obs.
Calc.
T=0.5K
1 MHz
2
2
1
Ab-initio predictions for LA+ 2 x H2O:
- 71.8
IaIb
IaIc
- 64.4
- 66.0
In fact:
dw-I
- 87.8
Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010)
The J = 7  6 transition of LA+2H2O:
a-type
2
5
4 4
3
3
2
1
Calc. T=1K
*
717  606
0
707  616
Ka = 1
b-type
The J = 10  9 aR-type transition of LA+3H2O:
Ka = 1
0
Calc. T=1K
2
6
55
3
4
4
1
3
2
Constants for the lactic acid+water clusters:
LA+H2O
PC-GAMESS, MP2/aug-cc-pVDZ
quartics  FCONV + VIBCA
LA+2H2O
aR-
Large cycle
LA+3H2O
and bR-type lines in all cases
sometimes also bQ-types
BSSE calculated binding energies (kJ/mol):
3-body = 22%
- 36.0
- 14.6
- 41.8
- 87.8
- 18.9
- 32.1
- 14.2
- 121.9
- 15.2
- 13.8
≥ 3-body = 38%
Binding energies and H-bond lengths:
2.652 Å
2.710 Å
2.809 Å
2.796 Å
2.621 Å
2.798 Å
Comparison with water clusters:
all at MP2/aug-cc-pVDZ
2.710 Å
2.921 Å
(H2O)3 2.803 Å
2.706 Å
(H2O)4 2.748 Å
2.720 Å
SUMMARY:
 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+H2O, LA+2H2O, LA+3H2O assigned (either classically
or using the “3-line” autofitting program (TC10, 65th 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.
 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)