Transcript Puzzarini_H2O17-ldip.ppt

ABSOLUTE 17O NMR SCALE:
a JOINT ROTATIONAL SPECTROSCOPY
and QUANTUM-CHEMISTRY STUDY
Cristina PUZZARINI and Gabriele CAZZOLI
Dipartimento di Chimica “G. Ciamician”, Università di Bologna
Michael E. HARDING and Jürgen GAUSS
Institut für Physikalische Chemie, University of Mainz
Columbus — June 26, 2009
1) Experiment:
Instrument & Technique
FREQUENCY RANGE covered @ LMSB
(1) 8-120 GHz (wave-guide Stark cell – P band)
(2) 50-600 GHz (from fundamental to the 6th harmonic)
+ 600-800 GHz (8th harmonic)
(3) 1.0-1.2 THz (9th harmonic)
+ 1.33-1.6 THz (12th harmonic)
MILLIMETER-WAVE EXPERIMENTAL SET-UP
(2) BLOCK DIAGRAM OF THE 50-800 GHz SPECTROMETER
fG
InSb
DETECTOR
MULTIPLIER
GUNN
DIODES
THERMOSTAT
or liquid N2 system
fG
MIX
MULT
90 MHz
|fG - mfRF |
fRF
GUNN P. SUPPLY
and
SYNCR
ref: 73 MHz
20 MHz
|fRF - nfS|
HP8642A
SYNTH
RF OSCILL
3.7- 7.6 GHz
corr
MIX
ref
SYNCR
LOCK - IN
10 MHz
freq. standard
ref: 20 MHz
nfS
MULT
fS
PREAMPL
SYNTH
10 kHz-1 GHz
Measurements: Lamb-dip technique
Using free-space cell
Polarizer
Corner cube
mirror
Cell
Scheme of the radiation path
InSb detector
Frequency
modulated
source
G. Cazzoli & L. Dore, J. Mol. Spectrosc. 143, 231 (1990).
Measurements: Lamb-dip technique
 obs   0 1  v za / c 
 obs
-vza
 vz 
  0 1  
c 

 obs   0
1) Partial saturation
2) Only Doppler profile
3) Rad: back and forward
+vza
vz= 0
()

Lamb-dip effect
Measurements: Lamb-dip technique
C18O: J = 1-0
CH2BrF
28 kHz
Doppler
the Lamb-dip technique allows
Doppler profile
1)DipToprofile
well resolve hfs (/ = 3.9x107,  =16 kHz)
2) To accurately determine
- frequencies
Lamb-dip
- hfs parameters
539120
539125
539130
539135
FREQUENCY (MHz)
109782.0
109782.1
109782.2
Frequency (MHz)
109782.3
109782.4
539140
GHOST TRANSITIONS
13
CO J = 1 - 0
F = 1/2-1/2
ghost
F = 3/2-1/2
2) Theory:
Computational details &
requirements
Parameters of Rotational Spectroscopy
Rotational Hamiltonian
Rotational constants
Spin-rotation interactions
Nuclear quadrupole coupling constants
Spin-spin (direct)
interactions
Effective Hamiltonian: determination of HRot via quantum chemistry
Quantum-Chemical Calculation
of Spectroscopic Parameters
• Nuclear quadrupole coupling
ELECTRIC FIELD GRADIENT
first-order property: requires first derivatives of energy
• Spin-rotation interaction
second-order property: requires second derivatives of energy
Quantum-Chemical Calculation
of Spectroscopic Parameters
• Spin-spin coupling
DIPOLAR SPIN-SPIN COUPLING TENSOR
requires equilibrium geometry: no „electronic property“
addditional contribution due to:
 indirect spin-spin coupling (usually negligible)
 vibrational corrections (anharmonic force field)
Beyond the Rigid-Rotator Approximation
COUPLING of ROTATIONAL and VIBRATIONAL MOTION
PERTURBATION THEORY starting from
the rigid-rotator harmonic oscillator approximation
 Vibrational corrections to properties:
KL
D KL  Deq


r
  D KL 
1

 Qr 
 Q 
2
r Q 0

  2 D KL 

 Qr Qs  ...
 Q Q 
r ,s 
r
s Q 0

Vibrational corrections require:
anharmonic force field calculations
Accurate hyperfine parameters
>>>> Main requirements:
- accurate method
- cc basis set
- CV corrections
Accurate hyperfine parameters
>>>> Main requirements:
- accurate method [CCSD(T)]
- cc basis set [nQ]
- CV corrections [additivity/CV bases]
Accurate hyperfine parameters
>>>> Main requirements:
- accurate method [CCSD(T)]
- cc basis set [nQ]
- CV corrections [additivity/CV bases]
- vibrational corrections
Accurate hyperfine parameters
>>>> Main requirements:
- accurate method [CCSD(T)]
- cc basis set [nQ]
- CV corrections [additivity/CV bases]
- vibrational corrections [ff: -correlated
method
-basis: nT]
3) Results
Lamb-dip spectra
recorded
Spectra analysis
& assignment
Hyperfine parameters
computed
Para lines
(IH,tot = 0)
hfs: only
17O
Hyperfine parameters ……….
17O:
H:
-nuclear quadrupole coupling
-spin-rotation
—
J = 3
1,3
- 2
2,0
EXPERIMENT
REAL
GHOST
REAL+GHOST
194000
194002
194004
FREQUENCY (MHz)
194006
J = 3
1,3
- 2
2,0
Experiment
Real
Ghost
Real+Ghost
193999.8
194000.1
FREQUENCY (MHz)
194000.4
Ortho lines
(IH,tot = 1)
hfs:
17O
+ H
Hyperfine parameters ……….
17O:
H:
-nuclear quadrupole coupling
-spin-rotation
-spin-spin (17O-H)
-spin-rotation
-spin-spin (H-H)
J = 1
1,0
- 1
0,1
EXPERIMENT
REAL+GHOST
REAL
GHOST
552018
552019
552020
552021
552022
FREQUENCY (MHz)
552023
J = 11,0 – 10,1
FREQUENCY (MHz)
Stick spectra:
REAL
GHOST
real+ghost
real
ghost
552021.0
552021.3
552021.6
J = 11,0 – 10,1
FREQUENCY (MHz)
Stick spectra:
REAL
GHOST
real+ghost
real
ghost
552021.40
552021.45
552021.50
J = 4
1,4
- 3
2,1
Experiment
Real+Ghost
Real
Ghost
385784
385786
385788
FREQUENCY (MHz)
385790
Results …….
17O
Experiment
Theory
Caa
-28.86(11)
-28.18
-28.61
Cbb
-27.229(81)
-27.94
-27.99
Ccc
-18.422(54)
-18.46
-18.49
results in kHz
Method:
CCSD(T)
Equil.
(exp re)
Vib.
Corr.
(VPT2)
Vib.
Corr.
(DVR)
Total
(Eq+Vib)
basis
augCV6Z
augCV5Z
augCV5Z
Caa
-22.251
-5.933
-6.361
-28.184
-28.612
Cbb
-25.196
-2.741
-2.794
-27.937
-27.990
Ccc
-17.476
-0.988
-1.015
-18.464
-18.491
„Experimental“ Determination
of Absolute Shieldings
measure rotational spectrum
 experiment
extract nuclear spin-rotation constant
 Cv,J
subtract rovibrational corrections
 Ce
convert to paramagnetic shielding
 σepara
add calculated diamagnetic shielding
 σedia
add rovibrational corrections
 σv,J
consider temperature effects
 σ(T)
Results …… Absolute
[ppm]
 (dia)
calculated
 (para)
from exp
 (equil)
 (vib)
 (T)
 (300K)
17O
NMR scale
isotropic
416.4
-78.5
-338.1(3)
-11.7
-0.4
326.2(3)
Best theoretical estimate 325.6 ppm
Results …… the other hf parameters
[MHz/kHz]
Experiment
Theory
1.5aa (17O)
-13.3060(25)
-13.21
MHz
(bb-cc)/4 (17O)
-2.88509(52)
-2.85
MHz
1.5Daa (17O-H)
23.44(43)
23.64
kHz
(Dbb-Dcc)/4 (17O-H)
5.182(97)
5.11
kHz
1.5Daa (H-H)
-101.8(25)
-102.27
kHz
Caa (H)
-34.63(30)
-34.27
kHz
Cbb (H)
-30.78(25)
-31.16
kHz
Ccc (H)
-32.91(12)
-32.54
kHz
THANK YOU for your attention!!
Calculations performed
using
CFOUR:
http://www.cfour.de
NMR
nuclear quadrupole
coupling CQ
chemical
shift

direct dipolar
coupling
D
indirect spin-spin
coupling
J
connection
nuclear magnetic
shielding 
absolute shielding
scales
Ramsey-Flygare
equations
form of Hamiltonians:
coupling mechanism
vs
tensor rank
MW
nuclear quadrupole
coupling 
nuclear
spin-rotation
C
tensor spin-spin
coupling (rank 2)
C3
scalar spin-spin
coupling (rank 0)
C4
Bryce & Wasylishen, Acc. Chem. Res. 36, 327 (2003)
OLD
Absolute
17O
NMR Scale
Radioastronomical study (Bok globule B335)
Frerking, Langer, J. Chem. Phys. 74, 6990 (1981)
Absolute
17O
NMR Scale
OLD
C(17O)
-30.4(12)
C(vib)
-0.1
(para)
-483.7(172)
(dia)
445.1
(eq)
-38.7(172)
(vib)
-5.73
(T)
-0.35
(300K)
-44.8(172)
Best theoretical estimate -59.34 ppm
Wasylishen et al., JCP 84, 1057 (1984); Sundholm, Gauss, Schäfer JCP 105, 11051 (1996)
Absolute
NEW
17O
NMR Scale
New laboratory study using Lamb-dip technique
Cazzoli, Dore, Puzzarini, Beninati, Phys. Chem. Chem. Phys. 4, 3575 (2002)
Absolute
17O
NMR Scale
OLD
NEW
C(17O)
-30.4(12)
-31.61(4)
C(vib)
-0.1
-0.1
(para)
-483.7(172)
-501.8(6)
(dia)
445.1
445.1
(eq)
-38.7(172)
-56.7(6)
(vib)
-5.73
-5.73
(T)
-0.35
-0.35
(300K)
-44.8(172)
-62.7(6)
Best theoretical estimate -59.34 ppm
Wasylishen et al., JCP 84, 1057 (1984); Sundholm, Gauss, Schäfer JCP 105, 11051 (1996)