Time-resolved inner-shell photoelectron spectroscopy: From a bound molecule to an isolated atom

Abstract

Due to its element-and site-specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here we show that time-resolved innershell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH3I) is investigated by ionization above the iodine 4d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules. arXiv:1901.08937v1 [physics.chem-ph] 25 Jan 2019 0 +) [fs] Energy [eV] J=5/2, J =5/2 J=3/2, J =3/2 J=5/2, J =3/2 J=3/2, J =1/2 J=5/2, J =1/2 z z z z z

Spectroscopic Signature of Chemical Bond Dissociation Revealed by Calculated Core-Electron Spectra

“…While the predicted phenomena have not yet been fully resolved experimentally, 19 a confirmation of our predictions is well within the range of capabilities at current free electron laser facilities.…”

“…With femtosecond soft x-ray pulses from free-electron laser (FEL) and high-harmonic generation (HHG) sources now becoming available, [9][10][11][12][13][14][15] well established steady-state techniques like x-ray absorption spectroscopy, x-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) can be employed to follow ultrafast dynamics of molecules. [16][17][18][19][20][21] Both steady-state XPS and AES are element specific, since ionization edges of different elements lie hundreds of eV apart. The core electron binding energies, which are measured in XPS, additionally, show a high sensitivity to the local bonding environment of a specific atom in a molecule.…”

“…This reaction has been experimentally investigated in several studies. 8,19,26,27,[30][31][32] The molecule is therefore an ideal benchmark for the capabilities of time-resolved XPS and AES. Photoexcitation of methyl iodide in the ultraviolet (UV) spectral regime leads to a single electron transition from an iodine-centered π molecular orbital (MO) to a carbon-iodine antibonding MO (π → σ * excitation).…”

“…26,27,30,31,[34][35][36][37] The photodissociation dynamics of methyl iodide have been experimentally investigated by XPS in a seminal study at the iodine 4d edge. 19 The study identifies a time-dependent shift of the iodine 4d binding energy as the XPS signature of C-I bond dissociation. With our present study, we theoretically investigate the XPS and AES during photochemical C-I bond breaking in CH 3 I using ab initio wavepacket simulations combined with a complete description of the electronic structure in the photoionization and subsequent Auger decay process employing the XMOLECULE toolkit.…”

Coulomb explosion imaging of CH3I and CH2ClI photodissociation dynamics

“…The experimental results are also compared with similar research recently carried out on CH 2 BrI in order to explore the relationship between the photochemistry of these similar molecules. 17 The ultraviolet photodissociation of CH 3 I in its A-band has been thoroughly studied both theoretically and experimentally [18][19][20][21][22][23][24][25][26][27] and is a model system for understanding photofragmentation in the gas phase. The analogous photodissociation of CH 2 ClI has been the subject of fewer studies.…”