TWO-PHOTON TRANSITIONS IN THE LASER INDUCED FLUORESCENCE OF NO₃ BY FUKUSHIMA

Oka, Takeshi

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Title

TWO-PHOTON TRANSITIONS IN THE LASER INDUCED FLUORESCENCE OF NO₃ BY FUKUSHIMA

Author(s)

Oka, Takeshi

Issue Date

2023-06-19

Keyword(s)

Comparing theory and experiment

Abstract

Recently, Fukushima reported laser-induced fluorescence of the B²Ε' - X²Α'₂ transition from the vibrationless B²Ε' excited state of jet-cooled ¹⁴NO₃ and ¹⁵NO₃ in which two beautiful series of ν₄ progressions in the ground X²Α'₂ state have been identified. One of the progressions corresponds to transitions with vibrational symmetry a₁' - a₁' while the other with a₁' - e'. The former is the ordinary single-photon spontaneous emission given in Eq.(II,11) of Herzberg Vol.III, while the latter is not discussed in ordinary textbooks of spectroscopy. Here I propose that the latter is due to Raman-type laser stimulated two-photon processes that were commonly observed around 1970. Contrary to the previous assignments which invoke vibronic mixing between the B²Ε' and X²Α'₂ states, the 2-photon assignment leaves the vibrational angular momentum l₄ in the ground X²Α'₂ state a good quantum number except for the Δl = 3 mixing. Therefore the l₄ assignment and the vibrational structure are extremely simple as reported in the Fukushima paper. The calculation using the Kramers-Heisenberg formula indicates that the laser power density is sufficiently high to cause the two-photon process. The perfectly normal ν₄ progression suggests strongly that the ν₃ progression is also normal. This suggests that the so-called "Assignment I" in which the intensity of the ν₃ fundamental band is higher than that of the ν₃ + ν₄ combination band is more reasonable than the "Assignment II" in which a theoretical calculation gives the ν₃ band weaker than the ν₃ + ν₄ band by a factor of 60 and an experimental observation by ~ 2000.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

Text

Language

eng

Handle URL

https://hdl.handle.net/2142/122484

DOI

https://doi.org/10.15278/isms.2023.6688

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