High-resolution FTIR spectra of NO 2 and N 2O 4 in supersonic jet expansions and their rovibrational analysis

Abstract

High-resolution FTIR spectra of NO 2 and N 2O 4 in supersonic jet expansions both neat and seeded with argon are reported between 700 and 1800 cm −1 at an unapodized instrumental bandwidth of 0.0024 cm −1. The ratio of NO 2:N 2O 4 is strongly dependent on the seeding ratio with Ar but relatively insensitive to stagnation pressure. Neat expansions result in rotational temperatures around 100 K for both NO 2 and N 2O 4 while 22 K was reached for NO 2 in expansions with 90% Ar. The two spin components of the resolved fine structure of the NO 2 spectra show identical rotational temperatures. The rotational structure of N 2O 4 was partly resolved. A preliminary analysis of the rotational structure of the ν 11 fundamental of N 2O 4 gives a band centre at 1261.080 cm −1. Rotational constants of 0.218, 0.1222, and 0.0784 cm −1 obtained for the vibrational ground state suggest a NN bond length of 177 ± 2 pm. Ab initio predictions of Coriolis coupling parameters, vibrational frequencies and electric dipole transition moments are presented.