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

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

} 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 (118-378 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)

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 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

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’’ 240 361 481 601 cm-1

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

Improvement in fitting the 2n9 dyad:

Much better agreement of fitted and calculated inertial defects: true fit? effective fit A 12181.43(4) 12103.604 B 2764.715(2) 2766.017 C 2242.6229(9) 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: 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. Ka = 2 Ka = 1 Ka = 0 current prediction: A 11623.98 B 2776.906 C 2279.217 effective fit: A 11693.992(20) B 2775.8343(35) C 2274.8399(34)

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)