Rotation-Vibration Spectra of Diatomic and Simple Polyatomic Molecules with Long Absorbing Paths VI. The Spectrum of Nitrous Oxide (N2O) below 1.2μ

The photographic infra‐red spectrum of N₂O has been investigated with absorbing paths up to 4500 m atmos. Thirty‐four absorption bands have been found of which twenty‐three have been measured and analyzed in detail. Improved vibrational constants ω_i⁰ and X_ik have been determined which give a fair representation of all the bands. The remaining deviations which are outside the present limits of error are due to the effect of Fermi resonance between ν₁ and 2ν₂. Precise values of the rotational constants B_v1v2v3 have been determined for almost all vibrational levels involved in the observed bands. For the lowest vibrational level the six most accurately measured bands yield B₀₀₀=0.4191₂₅ cm⁻¹. In this case also the rotational constant D₀₀₀ representing the influence of centrifugal stretching has been determined: D₀₀₀=0.19₃×10⁻⁶ cm⁻¹. The value of B₀₀₀ is larger by 0.000091 than that derived from microwave data. From the B_v1v2v3 values the following values for the rotational constants α_i have been obtained, $${\alpha }_1{\text{=0.0017}}_0{\mathrm{\hspace{0.17em}\hspace{0.17em}\alpha }}_2{\text{=−0.0002}}_2{\mathrm{\hspace{0.17em}\hspace{0.17em}\alpha }}_3{\text{=0.0033}}_9.$$ These values allow the determination of the rotational constant in the equilibrium position B_e=0.4214₅ cm⁻¹ from which the moment of inertia in the equilibrium position is found to be I_e=66.39₇×10⁻⁴⁰ g cm². The deviations of the individual B_v1v2v3 values from those obtained from the formula $B_{{\nu }_1{\nu }_2{\nu }_3}{\mathrm{=B}}_e{\mathrm{-\alpha }}_1{\mathrm{(\nu }}_1+\frac{1}{2}{\mathrm{)-\alpha }}_2{\mathrm{(\nu }}_2{\text{+1)−α}}_3{\mathrm{(\nu }}_3+\frac{1}{2})$ are appreciably larger than would correspond to the errors of measurements and must be ascribed to the effect of the Fermi resonance.