The Simulation of Infrared Bands from the Analyses of Rotational Spectra: the 9ν9 and ν5ν9 hot bands of HNO3

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The results of millimeter and submillimeter wave rotational spectroscopy are used to simulate the complex structure of the 9ν9 (438cm−1) and ν5ν9 (421cm−1) hot bands. The comparison data were obtained with a high-resolution Bruker FTIR. The combination of the quality of these data and the complexity of the spectra of these interacting states represents a stringent test for the simulation. It is shown that the agreement is very good and that this approach is generally advantageous. From this simulation, the ratios of the transition dipole moments for the 9ν9 and ν5ν9 hot bands with respect to theν9 fundamental band were found to be 1.38(11) and 0.67(20), respectively. Using these results, the calculated integrated band intensities for the hot bands at 296K were determined to be Sv(2ν9–ν9)=1.63×10−18cm−1/(mol cm−2) and Sv5–ν9)=0.36×10−18cm−1/(mol cm−2). These results were used to successfully simulate high-resolution stratospheric spectra obtained from a balloon flight of the FIRS-2 spectrometer. The more general problem of the rotation–vibration database and the optimal use of both microwave and infrared data to define it is discussed. It is concluded that it is best if the combination of data takes place at the level of the original spectra.