Authors: Elwood, S.A.; Simeonsson, J.B.

Source: Applied Spectroscopy, Volume 54, Issue 2, Pages 52A-77A and 159-330 (February 2000) , pp. 190-196(7)

Publisher: Society for Applied Spectroscopy

Abstract:

The relative merits of five laser excitation schemes have been evaluated for photoionization spectrometry (PIS) measurements of NO in air. All five schemes utilize wavelengths near 215 nm, which correspond to excitation of rovibronic transitions in the Alpha ²Sigma⁺ - Chi ²Pi_i (1,0) bands of NO. Photoionization of the excited NO molecules is accomplished by using wavelengths ranging from 215 to 1064 nm. Excitation spectra of the five PIS schemes reveal a significant enhancement when 355 nm radiation is used for photoionization. The enhancement is hypothesized to be related to a resonance or near-resonance ionization process for selected lines in the Alpha ²Sigma⁺ - Chi ²Pi_1/2 band [specifically the R₁₁ + Q₂₁ (J" = 8.5-12.5) lines and the P₂₁ + Q₁₁ (J" = 9.5-10.5) lines] and the Alpha ²Sigma⁺ - Chi ²Pi_3/2 band [specifically the R₁₂ + Q ₂₂ (J" = 8.5-12.5) lines and the P₂₂ + Q₁₂ (J" = 9.5-10.5) lines] of NO. Comparison measurements using all five schemes demonstrate that the highest sensitivity and highest signal-to-noise ratios are observed by using the 215 nm + 355 nm scheme, for which a limit of detection of 80 parts per trillion by volume for NO in air has been achieved.

Keywords: PHOTOIONIZATION; EXCITATION SCHEME

Document Type: Research article

DOI: http://dx.doi.org/10.1366/0003702001949384

Publication date: 2000-02-01

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