Two laser beams in the visible or ultraviolet region were converted to a vacuum ultraviolet (VUV) laser beam in a nonlinear optical medium of Sr and Mg vapor through a mechanism of the 2-photon resonant 4-wave sum mixing. The generated VUV laser beam was introduced into a vacuum chamber and the laser induced fluorescence (LIF) spectra of NO and CO cooled in the supersonic jet were measured. The rotational structure of the LIF spectra were presented for the following transitions: D
2Σ
+_X
2II (0, 0) for NO, A
1II-X
1Σ
+ (υ′, 0) (υ′=0-3), d3Δ
1-X
1Σ
+ (5, 0), and e
3Σ-_X
1Σ
+ (1, 0) for CO. In the case of CO, it was demonstrated that forbidden intercombination bands could be observed free from the hindrance of the intense A-X bands.
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