Spectral dependence of photoemission in multiphoton ionization of NO₂ by femtosecond pulses in the 375–430 nm range

Abstract

We investigate the multiphoton ionization of NO using tunable (430-375 nm) femtosecond pulses and photoelectron-photoion coincidence momentum spectroscopy. In order to understand the complex electronic and nuclear photodynamics at play following absorption of three to five photons, we also report extended photoionization calculations using correlated targets and coupled channels. Exploring the multiphoton dissociative ionization (MPDI) and multiphoton ionization (MPI) processes over such a broad energy range enables us to lend further support to our work carried out around 400 nm of a femtosecond laser [S. Marggi Poullain et al., J. Phys. B: At., Mol. Opt. Phys., 2014, 47, 124024]. Two excitation energy regions are identified and discussed in terms of the proposed reaction pathways, highlighting the significant role of Rydberg states, such as the [R*(6a), 3pσ] Rydberg state, in the NO multiphoton excitation and photoionization. These new results support our previous assumption that different bent and linear geometries of the NO(XΣ) ionic state contribute to the MPDI and MPI, consistent with the reported calculations which reveal an important vibronic coupling characterizing the photoemission. Remarkably, the strong anisotropy of the recoil frame photoelectron angular distribution (RFPAD) previously observed at 400 nm appears as a fingerprint across the whole explored photon energy range.

Dissociation of High-Lying Electronic States of NO2+ in the 15.5–20 eV Region

“…Various experimental methods including photoabsorption spectroscopy, , He I/He II photoelectron spectroscopy (PES) ,, and pulsed-field ionization zero-electron kinetic energy spectroscopy (PFI-ZEKE) have been utilized to characterize the cationic structure and spectroscopy, and much information has been obtained. The NO 2 + cation in excited electronic states is not stable and its dissociation has also been studied by a broad range of theoretical , and experimental methods like photoionization mass spectrometry (PIMS), , vector correlation (full dual 3D momentum correlation spectroscopy), , photoelectron photoion coincidence (PEPICO) spectroscopy, − and threshold photoelectron photoion coincidence (TPEPICO) spectroscopy, , all of which reported a rich and complex dissociation landscape.…”

Coherent two-dimensional electronic mass spectrometry

“…This is in line with previous multiphoton-ionization spectra of NO 2 that identified the dominant ionization pathway via a resonantly enhanced step at the three-photon level 41 . Ionization using four photons is accompanied with a change from bent to linear geometry at a resonant intermediate level 42 , 43 that can possibly proceed during the waiting time of T = 100 fs. This process could in principle be followed by scanning T which was not done here due to a considerable increase in measurement time.…”

Trends in angle-resolved molecular photoelectron spectroscopy

“…NO 2 induced by 400 nm femtosecond pulses, accounting for the partial molecular alignment subsequent to ( n − 1) photon absorption. 133,327…”

“…NO 2 induced by 400 nm femtosecond pulses, accounting for the partial molecular alignment subsequent to (n À 1) photon absorption. 133,327 Structured RFPADs have been reported for single photon ionization of the (1t 1 ,4t 2 ,1e) outer MOs of the CF 4 molecule dissociating into CF 3 + + F, for a recoil axis parallel to the polarization. 328 For e.g.…”