Tracing the 267 nm-Induced Radical Formation in Dimethyl Disulfide Using Time-Resolved X-ray Absorption Spectroscopy

Abstract

Disulfide bonds are pivotal for the structure, function, and stability of proteins, and understanding ultraviolet (UV)-induced S−S bond cleavage is highly relevant for elucidating the fundamental mechanisms underlying protein photochemistry. Here, the near-UV photodecomposition mechanisms in gas-phase dimethyl disulfide, a prototype system with a S−S bond, are probed by ultrafast transient X-ray absorption spectroscopy. The evolving electronic structure during and after the dissociation is simultaneously monitored at the sulfur L 1,2,3-edges and the carbon K-edge with 100 fs (FWHM) temporal resolution using the broadband soft X-ray spectrum from a femtosecond high-order harmonics light source. Dissociation products are identified with the help of ADC and RASPT2 electronic-structure calculations. Rapid dissociation into two CH 3 S radicals within 120 ± 30 fs is identified as the major relaxation pathway after excitation with 267 nm radiation. Additionally, a 30 ± 10% contribution from asymmetric CH 3 S 2 + CH 3 dissociation is indicated by the appearance of CH 3 radicals, which is, however, at least partly the result of multiphoton excitation.

Non-Orthogonal Configuration Interaction with Single Substitutions for Core-Excited States: An Extension to Doublet Radicals

“…The NOCIS simulation of the NO N K-edge spectrum. This spectrum has a Gaussian broadening of .25 eV and a Lorentzian broadening of .2 eV, consistent with previous work 76. See…”

A combined multi-reference pump-probe simulation method with application to XUV signatures of ultrafast methyl iodide photodissociation

“…As a probe within ultrafast pump-probe measurements, XAS is particularly attractive for revealing mechanistic details of photo-induced chemical reactions by following the time-evolution of various chemical groups through changes in their associated spectral features. There has been significant growth recently in application of table-top XUV/X-ray transient absorption spectroscopy [1][2][3][4][5] to probe valence and Rydberg core-excited states due to advances in high harmonic generation (HHG). A range of ultrafast photo-induced chemistry, such as bond breaking, 3,5 ring opening, 2,6 internal conversion (IC), and intersystem crossing (ISC), 4 has been studied with the aforementioned method.…”

“…There has been significant growth recently in application of table-top XUV/X-ray transient absorption spectroscopy [1][2][3][4][5] to probe valence and Rydberg core-excited states due to advances in high harmonic generation (HHG). A range of ultrafast photo-induced chemistry, such as bond breaking, 3,5 ring opening, 2,6 internal conversion (IC), and intersystem crossing (ISC), 4 has been studied with the aforementioned method. The bond breaking dynamics of CH 3 I has been studied for a few decades with different experimental methods, such as photofragment spectroscopy, 7 magnetic circular dichroism spectroscopy, 8 mass spectrometer, 9 velocity map imaging spectroscopy, [10][11][12][13] and so forth.…”

Ultrafast X-ray Transient Absorption Spectroscopy of Gas-Phase Photochemical Reactions: A New Universal Probe of Photoinduced Molecular Dynamics

“…TRXAS of photoexcited DMDS reveals an ultrafast S-S bond fission to form methylthiyl radicals. 36 Similarly, a C-I bond photodissociation of CH 2 ICl at 266 nm (S 0 →S 1 ) allows the characterization of the CH 2 Cl radical at both the chlorine L 2,3 -and carbon K-edges. 37 The NEXAFS of DMDS ( Figure 5a) shows a very rich spectrum at the sulfur L 2,3 edge and somewhat simpler spectra at the sulfur-L 1 and carbon-K edges.…”