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.
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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
66th OSU International Symposium on Molecular Spectroscopy WH1066th OSU International Symposium on Molecular Spectroscopy WH10
Lactic acid primer:
SsC (most stable conformer) a = 1.44 D b =
1.83 D
GskC +8.0kJ/mol 3.6% @298K
G’sk’C +8.6 2.9%
AaT +10.0 1.6% Gauche
matrix isolation ir + ab-initio, Borba,Gomez-Zavaglia,Lapinski,Fausto, less stable conformers PCCP 6, 2101 (2004)
MMW of SsC Pszczolkowski et al., J.Mol.Spectrosc. 234, 106 (2005)
ab-initio, LA+H2O Sadlej et al., PCCP 8, 101 (2006)ab-initio, LA+nH2O 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 !
• Rev.Sci.Instrum. 79, 053103 (2008)
Enhancements:
- Several nozzles- Multiple chirps on
one gas pulse
Analysis tools: AABS package + SPFIT/SPCAT:
Line blanking
Chirped pulse spectrum of Lactic acid (+H2O):
LA, SsC
LA, AaT
LA+H2O
LA+(H2O)2
(H2O)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
DE = +10.0 kJ/mol 1.6% @298K
B3LYP/6-311++G(d,p)
Relative intensities of SsC and AaT transitions:
Obs.
Calc.
212 ← 111 202 ← 101 211 ← 110
1 MHz
SsC AaT SsC AaT SsC AaT
Calculation with: a = 1.44 D for SsCa = 5.05 D for
AaT and AaT = 2% of SsC
AaT
Constants for the lactic acid monomers:
PC-GAMESS, B3LYP/6-311++G(d,p)
quartics FCONV + VIBCA
20 aR-type lines7 bR- and bQ-type
sfit = 12.1 kHz
SsC
Ab-initio predictions for LA + H2O:Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010)MP2/aug-cc-pVDZ
Ia Ib
Ic
- 31.6
- 22.9Most stable form with total binding energy
- 40.9 kJ/mol
The J = 4 3 aR-type transition of LA+H2O:
Obs.
Calc.T=0.5K
Ka = 1 0 2 2 1
1 MHz
Ab-initio predictions for LA+ 2 x H2O:
Smaga,Sadlej, J.Phys.Chem.A 114,4427(2010)
IaIb IaIc
dw-I
- 71.8
- 64.4
- 66.0
In fact:
- 87.8
The J = 7 6 transition of LA+2H2O:
Ka = 1 0 2 5 4 4 3 3 2 1
Calc. T=1K
a-type
7 07
61
6
7 17
60
6
b-type
*
The J = 10 9 aR-type transition of LA+3H2O:
Ka = 1 0 2 6 55 3 4 4 1 3 2
Calc. T=1K
LA+3H2OLA+2H2O
Constants for the lactic acid+water clusters:
PC-GAMESS, MP2/aug-cc-pVDZ
quartics FCONV + VIBCA
aR- and bR-type lines in all casessometimes also bQ-types
LA+H2O
Large cycle
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%
Binding energies and H-bond lengths:
2.621 Å
2.798 Å
2.652 Å
2.796 Å2.710 Å
2.809 Å
Comparison with water clusters:
2.921 Å 2.710 Å
2.706 Å
2.720 Å
(H2O)3 2.803 Å
(H2O)4 2.748 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+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)
SUMMARY:
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