Comment on Electronic, vibrational and torsional couplings in N-methylpyrrole: Ground, first excited and cation states [J. Chem. Phys. 154, 224305 (2021)]

Two-color (1 + 1') zero-electron-kinetic-energy (ZEKE) and photoionization efficiency (PIE) spectra are reported via different levels in the S-1 <- S-0 ((A) over tilde (1)A(2) <- (X) over tilde (1)A(1)) one-photon transition of jet-cooled N-methylpyrrole. The laser radiation is produced using two dye lasers, one with an 1800 l/mm grating and one with 2400 l/mm. We report spectra where the excitation and ionization radiation are produced with both combinations of the dye lasers; these spectra differ markedly. This is attributed to Wood's anomalies with the 2400 l/mm grating: one aspect is a loss in light intensity over a range of wavelengths, attributed to a resonance anomaly. Another is the appearance of a shadow ZEKE spectrum and PIE curve at apparently higher ionization wavenumbers; under some conditions, a third ZEKE spectrum was observed-these latter observations arise from higher-order dispersion effects, likely caused by a Rayleigh anomaly. We comment on these observations and report more representative ZEKE and PIE spectra than those presented in a recent paper by our group [A. R. Davies, D. J. Kemp, and T. G. Wright, J. Chem. Phys. 154, 224305 (2021)] for four intermediate S-1 levels. Published under an exclusive license by AIP Publishing.

Automated summary

Two-color ZEKE and PIE spectra were reported for the S-1 <- S-0 transition of N-methylpyrrole, produced using dye lasers with different gratings. The anomalies observed with the 2400 l/mm grating led to distinct features in the spectra, including additional ZEKE and PIE curves attributed to higher-order dispersion effects.