Transcript clono2_2008.ppt

63rd OSU International Symposium on Molecular Spectroscopy
FC01
The rotational spectrum of chlorine nitrate
(ClONO2) in the three lowest nn9 polyads
Zbigniew Kisiel, Ewa Białkowska-Jaworska
Institute of Physics, Polish Academy of Sciences
Rebecca A H Butler Department of Physics, Pittsburgh State
University, Douglas T. Petkie, Department of Physics, Wright
State University, Paul Helminger, Department of Physics,
University of South Alabama, Frank C. De Lucia, Department of
Physics, The Ohio State University
The chlorine nitrate molecule ( ClONO2 ) :
5 atoms
9 normal modes
ma = 0.72(7) D
mb = 0.24(2) D
Takes part in several stratospheric processes:
ClO + NO2 + M  ClONO2 + M
ClONO2 + HCl  Cl2 + HNO3
ClONO2 + H2O  HOCl + HNO3
Studies of the FASSST rotational spectrum of ClONO2:
E
/cm-1
< 840 cm-1
R.A.H.Butler, PhD Dissertation,
OSU (2002)
g.s., n5/ n6n9: J.Mol.Spectrosc. 243, 1 (2007)
n9, n6:
J.Mol.Spectrosc. 244, 113 (2007)
2n9 / n7 :
3n9 / n7n9 :
J.Mol.Spectrosc. 213, 8 (2003)
J.Mol.Spectrosc. 220, 150 (2003)
Present study (118-378 GHz spectrum):
2n9 / n7
revisited
3n9 / n7n9
4n9 / n72n9 / 2n7
main study
5n9 / n73n9 /2n7n9 check of the procedures
}
FASSST = FAst Scanning Submillimeter Spectroscopic
Technique
Developed 1997 at OSU:
coverage: 110 - 370 GHz
speed: < 1s per 10 GHz
AABS = Assignment and Analysis of Broadband Spectra
(available on the PROSPE website)
Summary of predictions loaded into AABS:
Problems with inertial defects:
Di = Ic- (Ia + Ib)
in units of u Å2
Interstate interactions in the nn9 polyads:
All levels in a given polyad belong to the same representation of the Cs point
group, either A’ or A’’. Now:
A’  A’ = A’ and A’’  A’’ = A’.
Since A’ contains the rotation Rc there will be Coriolis interaction around the
inertial c-axis. Fermi interaction is also possible.
2n 7
2 n 7n 9
A’
A’’
n7
n 7n 9
n 7 2n 9
n 7 3n 9
A’
A’’
A’
A’’
2n 9
3n9
4n 9
5n 9
A’
A’’
A’
A’’
240
361
481
c-axis Coriolis
and Fermi
c-axis Coriolis
and Fermi
601 cm-1
The Hamiltonian for the nn9 polyads:
This will be in block form. Each state will have a diagonal block for the
rotational Hamiltonian and its vibrational energy or energy separation DE.
The off-diagonal blocks will consist of terms for c-axis Coriolis interaction
between states i and j :
Hc(i , j) = (Gc + GcJ + GcK + …) Pc +
(Fab + FabJ + GabK + …) (Pa Pb + Pb Pa ) + …
and for the Fermi interaction:
HF(i , j) = F0 + F J P 2 + F K Pz 2 + …
Previous problems:
Current problems:
Coriolis expansion started at second order Fab terms,
no Fermi interaction but instead an assortment of more
exotic terms
Considerable correlation problems between DE and F0
Improvement in fitting the 2n9 dyad:
Much better agreement of fitted and calculated inertial defects:
A
B
C
true fit?
effective fit
12181.43(4)
2764.715(2)
2242.6229(9)
12103.604
2766.017
2247.233
Data distribution plots for the 4n9 triad in 35ClONO2:
Circle diameters  obs-calc
red circles for o-c > 0.3 MHz
3456 lines in fit
54.9 kHz deviation of fit
The fit for the 4n9 triad in 35ClONO2:
no need
to fit sextic or
higher c.d.’s
Evolution of coupling constants in the n n9 polyads:
0
F0
F0
DE
-DE12 F12 0
F12 0 F23
0
F23 DE23
Prediction of 5n9
by extrapolation
from coupled fits:
Loomis-Woods type plots
for R-branch transitions
using the actual spectrum.
The values of J’’ are
indicated to the right of
each plot.
current prediction:
A
B
C
11623.98
2776.906
2279.217
effective fit:
A
B
C
11693.992(20)
2775.8343(35)
2274.8399(34)
Ka = 2
Ka = 1
Ka = 0
Conclusions from the analysis of the n n9 polyads in ClONO2 :
 Exercise considerable care in constructing the Hamiltonian.
 In the presence of strong interactions the solution space is highly nonlinear and
it is very difficult to switch fitting models (and to find the global solution).
 Well chosen Hamiltonian results in the simplest solution, but it may be difficult
to distinguish between models entirely on the basis of sfit and Nlines in fit
 Use as many checks as possible. In the present case the ab initio calculated
inertial defects were crucial. Calculated Coriolis coefficients and energy level
separations are also useful. It is important to monitor changes in values of c.d.
constants from those in the ground state.
 All 11 vibrationally excited states below 600 cm-1 have now been analysed for
both 35ClONO2 and 37ClONO2 (making 14 states below 650 cm-1 on completion
of analysis for the 5n9 triad).
The nn9 polyads account for the majority of these states  7 out of 11
(10 out of 14)