Transcript Columbus_2006_Acetol_Lactonitrile.ppt

Combined Microwave and Millimeter
Wave Studies of the Molecules
Hydroxyacetone and Lactonitrile
ALDO J. APPONI, JAMES J. HOY and LUCY M. ZIURYS
LAPLACE ASTROBIOLOGY CENTER
UNIVERSITY OF ARIZONA, STEWARD OBSERVATORY, TUCSON, AZ 85721
MATTHEW A. BREWSTER
SFYRI Inc., Seattle, WA, 98109.
Ab Initio calculations by:
ABRAHAM F. JALBOUT and LUDWIK ADAMOWICZ
LAPLACE ASTROBIOLOGY CENTER
UNIVERSITY OF ARIZONA, DEPT. OF CHEMISTRY, TUCSON, AZ 85721
Why these two molecules?
• Test out the newly built FTM Spectrometer
– Hydroxyacetone started in March 2005
• Astrophysical implications
– Exhibits the next level of complexity for “sugar” type molecules
– Difficult methyl top problem—could account for U-lines
– Similar to the recently discovered acetamide
• We supposedly knew the frequencies
• High vapor pressure liquid easy to get in the gas
• First of two papers just submitted (or just about to be)
– Lactonitrile started a few days before the deadline
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•
•
•
•
Another methyl top, but this one has no resolved E-species
Hyperfine practically gives away the microwave lines
High vapor pressure liquid easy to get in the gas phase
Two stable conformers (dynamical spectroscopy)
Astrophysically relevant acetaldehyde cyanohydrin
Previous Studies
• Hydroxyacetone
– Kattija-Ari and Harmony 1980 (Inter. J. Quan.
Chem.:Quant. Chem. Sym., 14, 443)
•
•
•
•
A-state 26 to 40 GHz (43 lines)
E-state (10 lines; several misassigned)
Dipole moments (ma = 2.22 D; mb = 2.17 D)
Low Barrier internal methyl rotor
– Braakman, Drouin, Widicus and Blake 2005
(60th Inter. Sym. on Mol. Spec.)
• A-state 85 to 115 and 220 to 376 (578 lines)
• E-state (288 lines)
• Astronomical search 1 mm (Ntot < 8x1014 cm-2)
Previous Studies: Lactonitrile
• Acetaldehyde cyanohydrin
• Corbelli and Lister 1981 J. Mol. Struct., 74, 39
– Two stable gauche rotamers
– Measured a few a-type transition in each between 13 and
37 GHz
– Course rotational constants
– Not much structural information
• Their gauche rotamers were approximately correct
Ab Initio Calculations: Hydroxyacetone
MP2/6-311+G** Geometry Optimization
CCSD (T)/6-311+G** Single Point Calcs.
Conformer II not stable
Methyl rotation barrier ~57 cm-1
Ab Initio Calculations: Lactonitrile
1180 cm-1
115 cm-1
FTM Spectrometer
20” mirrors (4 to 20 GHz operation)
Upgrade to 40 GHz by August
Complete computer control and tuning
NI timing electronics and DAQ
Modified FTMW++ (Jens Grabow)
Two 8” gate valves for nozzle
Radiation/magnetic shield planned
22” cryopump (14000 liters/sec Ar)
Linear Actuator
Mirror sled
Microwave Data: Hydroxyacetone
46 microwave lines were measured to an accuracy of about 2 kHz
S/N > 100 on most of the lines
Microwave lines were necessary for assigning the millimeter wave data
and to “lock-in” the E-state parameters
400
200
Intensity (mV)
Intensity (mV)
400
0
-200
-400
0
-400
-600
50
100
150
Tim e (m icros ecs )
30
20
10
200
Acetol A
30,3 – 20,2
40
Intensity (mV)
40
100
150
Tim e (m icros ecs )
50
Acetol E
30,3 – 20,2
50
Intensity (mV)
50
200
30
20
10
19422.0
19422.2
Frequency (MHz)
19422.4
19670.0
19670.2
19670.4
Frequency (MHz)
19670.6
Millimeter Wave Data
Covered 65 to 175 GHz contiguously
Stitched together ~1800 spectra with a total of 1,150,000 data points
Each scan took about 5 minutes to acquire
Room temperature spectrum strong above 120 GHz owing to the collapsed
asymmetry splittings
Strongest lines separated by about (B+C) or 4 GHz
Hydroxyacetone J = 16 to 21
E
A
Rho-axis method Hamiltonian
Rotation-Torsion Hamiltonian
r-Axis Method (RAM)
Hˆ  Hˆ rot  Hˆ tors  Hˆ dist
Hˆ rot  1 2 ( B  C)(Pˆb2  Pˆc2 )  APˆa2  1 2 ( B  C)(Pˆb2  Pˆc2 )  Dab ( Pˆa Pˆb  Pˆb Pˆa )
Hˆ tors  F ( Pˆ  rPˆa ) 2  1 2 V3 (1  cos 3 )
RAM code provided by Isabella Kleiner
History of the code:
C
C
I.KLEINER AND M.GODEFROID (FREE UNIVERSITY OF BRUSSELS,
50, AV. F-D. ROOSEVELT, 1050 BRUSSELS, BELGIUM, 1987-91)
C jth added two cards here
C
C
C
30 sep MAB Today is the end of the common block.
4 oct 05 MAB - Implement torsional basis sorting of M.A. Mekhtiev and J.T. Hougen,
J. Mol. Spec., 187, 49-60, (1998), Ilyushin (2004), J. Mol. Spec., 227, 140
Eigenvector Labeling Problem
– “Old School” energy ordering doesn’t work for
energies above the barrier
– Since the levels are K-dependent, a given
torsional basis cannot be associated with a
single eigenvector
– Ask Jon Hougan at the Picnic
Fitted Rotational Constants for Hydroxyacetone
Leading order parameters (21 total parameters)
Parameter
Operator
This Work
Kattija-Ari et al.
V3
(1/2)(1-cos3) 65.3560(22) cm-1
68(4) cm-1
F
P2
159.1189(40) GHz
157.931 fixed
r
PPa
0.0587793(26) unitless
nd
A (diagonalized)
Pa2
10074.875(51)
10069.410(57)
B (diagonalized)
Pb2
3817.2550(90)
3810.412(8)
C (diagonalized)
Pc2
2866.6157(100)
2864.883(4)
Dab
{Pa,Pb}
1089.287(44)
nd
DI=Ic-Ia-Ib
6.5 amu Ǻ2
6.4 amu Ǻ2
Total number of lines
1145 (740 A; 405 E)
53
Microwave RMS
4 kHz
A-state 20 kHz
Millimeter wave RMS
90 kHz
E-state 9 MHz
Microwave Data: Lactonitrile
F =1 – 0
Image
Image
2
Image
F=1–2
F=2–1
I (mV)
4
F=1–1
F=2–2
8
6
JKa,Kc = 21,2 – 11,1
F=3–2
Lactonitrile
0
12932.0
12932.5
12933.0
12933.5
12934.0
Frequency (MHz)
Frequency
(MHz)
12934.5
12935.0
12935.5
Millimeter
Wave Data
II
I
1500
1000
500
0
J = 17
-500
103600
103700
103800
Calculated Dipole Moments
103900
104000
Conformer I:
ma = 2.32 D; mc = 1.67 D
600
400
200
Conformer II:
ma = 2.94 D; mb = 1.25 D
0
109600
109700
109800
109900
110000
1500
1000
500
0
Relative Energy (kcal/mol)
J = 18
-200
2.75
2.50
D E =2.10
ZPE=0.32
2.25
900 cm-1
D E=0.16
2.00
D E=1.51
1.75
J = 19
-500
115500
115600
115700
115800
1.50
115900
1.25
1.00
600
0.75
400
0.50
200
0.25
0
ZPE=0.35
115 cm-1
ZPE=0.28
ZPE=0.28
0.00
0
-200
J = 20
121500
121600
121700
121800
40
80
120
160
200
OH Rotation (Degrees)
121900
240
280
320
360
2(1,1) – 1(1,1)
F=3-2
6.00
Conf. I
5.00
4.00
Conformer I vs. II
Using normal backing pressure of 40
psia conformer II signals are
undetectable.
3.00
Reducing the backing pressure to
about 30 in of Hg above vacuum
reduced the signals of Conformer I by
a factor of 20, but allowed for the
detection of Conformer II signals in the
microwave.
2.00
1.00
0.00
12933.4
12933.5
Conf. II
0.20
0.15
115 cm-1 above ground
0.10
0.05
0.00
12992.4
12992.5
Lactonitrile Constants
Conformer I
Conformer I
Parameter
Experimental
Theoretical (MHz)
(MHz)
A
8790.20855(106)
8816
B
4005.854834(313)
3996
C
2975.800820(303)
2960
DJ
0.0009642(137)
DJK
0.012371(74)
DK
-0.004083(240)
δJ
-0.0002330(55)
δK
-0.007814(126)
Χaa
-4.08723(137)
Χaa-Χbb
0.51196(280)
mwave
0.0015
RMS
mm-wave
0.084
RMS
Conformer II
Experimental
(MHz)
8584.059(135)
4028.6686(306)
2987.8407(64)
0.0010006(296)
0.011287(37)
-0.00621(157)
-0.0002333(155)
-0.006935(125)
-4.053(45)
0.300(20)
0.005
0.031
Conformer II
Theoretical (MHz)
8596
3987
2971
Acknowledgements
• Thanks to Jens Grabow for the help
getting the FTMW++ software running
• Thanks to Isabella Kleiner for the Rho-axis
code