Abstract

The infrared spectrum of NO₂ has been reinvestigated in the 1.4–3.4μ region under high dispersion. The nine bands observed show resolvable rotational structure and the moments of inertia obtained, in conjunction with the large rotational constant from measurements of ν₂ by Wilson and Brown, yield the ground state parameters r_N–O=1.188±0.004A and ∢O—N—O=134° 4′±15′. The set of overtones and combinations observed together with ν₂=750.9 cm⁻¹ from Wilson and Brown allow one to determine a complete set of quadratic vibrational interaction constants. The fundamental frequencies of NO₂ are ν₁=1322.5 cm⁻¹, ν₂=750.9 cm⁻¹, and ν₃=1616.0 cm⁻¹. An intensity alternation is observed in type A bands as is predicted by theory but which, as far as the authors are aware, has not previously been observed in a similar case. An apparently abnormal interaction, which is not adequately explained, occurs between the vibrational levels 3ν₃ and 2ν₁+3ν₂ and likewise between ν₁+3ν₃ and 3ν₁+3ν₂.

© 1953 Optical Society of America

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