Pure Rotation Spectrum of NNO in the Far Infrared Region

Abstract

The pure rotational spectrum of NNO has been observed as an impurity in the NO spectrum which has been recorded with a high resolution Fourier transform spectrometer. The observed high-J transitions in the ground vibrational state were analyzed by a least-squares fit together with the available millimeter and submillimeter wave data. It has been proved that the highly precise data of Maki et al. [3] can be used as a wavenumber standard for the far infrared.Recently Maki and coworkers have revised the spectroscopic parameters of the NNO molecule intending to supply a good wavenumber standard in the infrared region [1][2][3]. They have measured the vibration-rotation transitions of this molecule in the infrared region with high precision by using heterodyne technique. They have provided also a very accurate set of the constants for the ground state [3]. However, to the best of our knowledge, the pure rotational transitions in the far infrared (FIR) have not been measured yet. In the course of our meaurements of NO [4], we have accidentally found the spectrum of NNO in the region from 20 to 50 cm ~~1 as an impurity. By analyzing these data together with the available millimeter (mmw) and submillimeter (sub-mmw) wave data [5,6] up to 552 GHz, we have confirmed the ground state constants of [3].The measurement has been carried out with a Bruker IFS 120 HR vacuum Michelson spectrometer at the molecular spectroscopy laboratory, Physikalisch-Chemisches Institut, Universität Giessen. The sample of NO was sublimated at a low temperature, in order to prevent contamination by water, and was transfered at a total pressure of about 150 Pa into the 1.8 m long cell sealed with polyethylene windows. The total pressure was around 156 Pa. The spectrum was recorded in the region from 20 to 90 cm -1 , using a myler beamsplitter and InSb detector at liq. He temReprint request to Dr. Koichi M. T. Yamada, I. Physikali-