Abstract
The electronic spectrum associated with the S1 ← S0 (Ã1A2←X̃1A1) one-photon transition of jet-cooled N-methylpyrrole is investigated using laser-induced fluorescence (LIF) and (1 + 1) resonance-enhanced multiphoton ionization (REMPI) spectroscopy; in addition, the (2 + 2) REMPI spectrum is considered. Assignment of the observed bands is achieved using a combination of dispersed fluorescence (DF), two-dimensional LIF (2D-LIF), zero-electron-kinetic energy (ZEKE) spectroscopy, and quantum chemical calculations. The spectroscopic studies project the levels of the S1 state onto those of either the S0 state, in DF and 2D-LIF spectroscopy, or the ground state cation (D0 +) state, in ZEKE spectroscopy. The assignments of the spectra provide information on the vibrational, vibration-torsion (vibtor), and torsional levels in those states and those of the S1 levels. The spectra are indicative of vibronic (including torsional) interactions between the S1 state and other excited electronic states, deduced both in terms of the vibrational activity observed and shifts from expected vibrational wavenumbers in the S1 state, attributed to the resulting altered shape of the S1 surface. Many of the ZEKE spectra are consistent with the largely Rydberg nature of the S1 state near the Franck-Condon region; however, there is also some activity that is less straightforward to explain. Comments are made regarding the photodynamics of the S1 state.
Highlights
The main focus here will be the vibrational and vibrationtorsional levels in the S0, S1, and D0+ electronic states of NMP, building on our earlier two-dimensional laser-induced fluorescence (LIF) (2D-LIF) and zero-electron-kinetic energy (ZEKE) study that concentrated on the torsional levels20 and where we reported the adiabatic ionization energy (AIE) as 64 250 ± 5 cm−1
Not emphasized in Ref. 20, we found the 2D-LIF spectrum recorded for the torsional levels of NMP to be dominated by 151mx and 161mx bands, at the positions where the mx transition was excited; this is consistent with activity seen for the vibrations
The ground state IR and Raman data, obtained from liquid, solution, and surface studies,23,24 were discussed in Ref. 33 and are presented in Table II; in Ref. 33, we presented calculated S0 values (B3LYP/aug-cc-pVTZ, scaled by 0.97), which were in very good agreement with the experimental values, and we discussed previously reported calculated values
Summary
Pyrroles, including N-methylpyrroles, are key building blocks of many biomolecules (e.g., tryptophan, haem B, melatonin, and phycobiliproteins), a range of medicines (including photomedicines), metalloporphyrin-based metal–organic frameworks (MOFs), and molecular wires. N-methylpyrrole (NMP) has been the subject of a number of photodissociation studies, which have compared and contrasted its behavior with that of pyrrole. A detailed understanding of the photophysics and photodynamics of molecules relies on establishing the energy-level structure; as such, there have been a number of spectroscopic studies of NMP.The absorption spectrum of gaseous NMP molecules at ambient temperature has been reported by Milazzo, McDiarmid and Xing, and Cooper et al. Spectra of supersonicjet-cooled molecules have been presented by McDiarmid and Xing, Philis, and Biswas et al.; suggested assignments of the S1 vibrational and torsional levels were given by Woo and Kim. A theoretical study of the torsional levels in NMP was published by Kanamaru, we have questioned some of the conclusions of that work.. N-methylpyrrole (NMP) has been the subject of a number of photodissociation studies, which have compared and contrasted its behavior with that of pyrrole.. A detailed understanding of the photophysics and photodynamics of molecules relies on establishing the energy-level structure; as such, there have been a number of spectroscopic studies of NMP. The absorption spectrum of gaseous NMP molecules at ambient temperature has been reported by Milazzo, McDiarmid and Xing, and Cooper et al.. Spectra of supersonicjet-cooled molecules have been presented by McDiarmid and Xing, Philis, and Biswas et al.; suggested assignments of the S1 vibrational and torsional levels were given by Woo and Kim.. A theoretical study of the torsional levels in NMP was published by Kanamaru, we have questioned some of the conclusions of that work.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
