1. 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

2. Takes part in several stratospheric processes:
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

3. } Studies of the FASSST rotational spectrum of ClONO2:
< 840 cm-1 R.A.H.Butler, PhD Dissertation, OSU (2002)
E /cm-1
g.s., n5/ n6n9: J.Mol.Spectrosc. 243, 1 (2007)
n9, n6: J.Mol.Spectrosc. 244, 113 (2007)
Present study ( GHz spectrum):
2n9 / n7 revisited
3n9 / n7n9
4n9 / n72n9 / 2n7 main study
5n9 / n73n9 / 2n7n9 check of the procedures }
2n9 / n7 : J.Mol.Spectrosc. 213, 8 (2003)
3n9 / n7n9 : J.Mol.Spectrosc. 220, 150 (2003)

4. FASSST = FAst Scanning Submillimeter Spectroscopic Technique
Developed 1997 at OSU:
coverage: GHz
speed: < 1s per 10 GHz

5. AABS = Assignment and Analysis of Broadband Spectra
AABS = Assignment and Analysis of Broadband Spectra (available on the PROSPE website)

6. Summary of predictions loaded into AABS:

7. Problems with inertial defects: Di = Ic- (Ia + Ib) in units of u Å2

8. 2n7 2n7n9 n7 n7n9 n7 2n9 n7 3n9 2n9 3n9 4n9 5n9 A’ A’’ A’ A’’ A’ A’’
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.
2n7 A’
2n7n9
A’’
c-axis Coriolis
and Fermi n7 A’
n7n9
A’’
n7 2n9 A’
n7 3n9
A’’
c-axis Coriolis
and Fermi
2n9 A’
3n9
A’’
4n9 A’
5n9
A’’
cm-1

9. Hc(i , j) = (Gc + GcJ + GcK + …) Pc +
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: Coriolis expansion started at second order Fab terms,
no Fermi interaction but instead an assortment of more
exotic terms
Current problems: Considerable correlation problems between DE and F0

10. Improvement in fitting the 2n9 dyad:

11. Much better agreement of fitted and calculated inertial defects:
true fit? effective fit
A (4)
B (2)
C (9)

12. Data distribution plots for the 4n9 triad in 35ClONO2:
Circle diameters  obs-calc
red circles for o-c > 0.3 MHz
lines in fit
54.9 kHz deviation of fit

13. The fit for the 4n9 triad in 35ClONO2:
no need
to fit sextic or higher c.d.’s

14. Evolution of coupling constants in the n n9 polyads:
F0 DE
-DE12 F12 0
F F23
0 F23 DE23

15. 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.
Ka = 2
Ka = 1
Ka = 0
current prediction: A B C
effective fit:
A (20)
B (35)
C (34)

16. 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)