Abstract

Fourier transform spectroscopy (FTS) was initially used mainly in infrared studies but has now been extended well into the visible and ultraviolet regions, where many advantages are found over classical grating spectroscopy. However, relatively stable sources are required for recording emission spectra. Microwave, radio frequency, and dc discharges through various gases can produce optical emissions from excited radicals, but these often have fairly complicated spectra. Simpler spectra can be obtained by combining FTS with other techniques. Laser excited fluorescence can be used with FTS in some cases and has been applied successfully to the transitions ${Ã}^2{A}_1\to {\tilde{X}}^2{B}_1$ and ${\tilde{\text{A}}}^{\text{2}}{\Sigma }^{+}\to {\tilde{X}}^{\text{2}}{\text{II}}_i$, of NCO. Cooled emissions, emitted from discharges through supersonic jets, are useful for simplifying dense spectra and were essential for the rotational analyses of both the b⁴Σ^– → a⁴II_i transition and the 5g → 4f Rydberg–Rydberg transition of NO. Chemiluminescence experiments using electronic energy transfer from metastable oxygen (a¹Δ_g) can produce very clean emission spectra from molecules with low-lying electronic states. Similarly, metastable He atoms can be used to generate excited molecular ions by Penning ionization; for example, ${\text{CO}}_2^{+}$ and H₂O⁺ formed in this way show intense electronic emission spectra with T_rot ≈ 300 K.

© 1989 Optical Society of America