THE NO DIMER, 14N AND 15N ISOTOPOMERS ISOLATED IN ARGON MATRIX : A NEAR-, MID-, AND FAR-INFRARED STUDY

A near- and far-infrared study of 14NO−14NO and its isotopomers, 14NO−15NO and 15NO−15NO, isolated in argon matrix has been carried out. Infrared active fundamental vibrational modes, ν1, ν2, ν3, ν5, and ν6, for each species of the dimer have been observed, as well as overtone bands 2ν1, 2ν5 and combination bands ν1 + ν5, ν1 + ν6, ν5 + ν6, and ν4 + ν5. Frequency of the nonactive ν4 mode was also retrieved from combination bands. From the knowledge of the 18 available frequencies of the three isotopic species, force constants for the cis-ON−NO have been calculated. The force constants characterizing the N−N stretching mode and the ONN bending mode are found to be 0.39 mdyn/A and 0.42 mdyn A/rad2, respectively. The potential energy distribution calculated for each vibration showed that the ν2 and ν3 modes are strongly coupled and that there is no pure N−N stretching mode. In the same way, the ν1 mode could be considered as a pure NO stretching mode while the ν5 one is coupled to the ONN bending.