Observation of highly vibrationally excited X̃ 1Σ+ HCP by stimulated emission pumping spectroscopy

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Abstract
We have recorded stimulated emission pumping (SEP) spectra of highly vibrationally excited methinophosphide (HCP) at 16 000 cm−1–19 000 cm−1 above the zero‐point energy of the linear X̃ 1Σ+ ground electronic state. These vibrational levels have most of their energy localized in the bending coordinate. The turning point in the bending vibration brings the H atom approximately halfway (∠HCP∼90°) from HCP to another chemical network, HPC. The SEP spectra of large‐amplitude‐bending states, (0,26,0), (0,28,0), and (0,30,0), and of bending–C≡P stretching combination states, (0,24,1) and (0,26,1), have enabled us to determine rotation–vibration spectroscopic constants for highly vibrationally excited X̃ 1Σ+ HCP. The rotational structure of HCP shows that B values change byg22 (eff ) constant, which reflects the energy difference between purely planar (l=0) versus slightly elliptical (l=2) bending, increases only 12% from (0,2,0) to (0,30,0), thus illustrating the surprisingly harmonic appearance of the vibrational motion even at this high energy.