Signature of a conical intersection in the dissociative photoionization of formaldehyde

Abstract

Electron/ion coincidence experiments and ab initio calculations of the dissociative photoionization of formaldehyde reveal the presence of a conical intersection controlling the dynamics and favoring dissociation into the molecular channel, CO+ + H2.

Impact of Nonzeolite-Catalyzed Formation of Formaldehyde on the Methanol-to-Hydrocarbons Conversion

“…13,21,23 By choosing the photoionization energy of hν = 10.9 eV, the fragmentation of formaldehyde could be suppressed, thus allowing for its selective detection in the presence of methanol and the MTH products. 25,36 In particular, the time-of-flight (TOF) mass spectra of the outlet reactor feed recorded at hν = 10.9 eV revealed that, besides the characteristic methanol peak at m/z 32 and its small 13 C satellite at m/z 33, an additional peak was also present at m/z 30 (Figure 1b). Because this photoionization energy is well below the dissociative ionization threshold of methanol, the m/ z 30 peak arises from formaldehyde.…”

“…This is largely caused by the challenging detection of formaldehyde in the MTH conversion, because of its low concentration and facile decomposition in gas chromatography and electron ionization mass spectrometry. 35,36 Similarly, interferences and tedious sample preparation complicate the formaldehyde analysis by alternative quantification methods, such as infrared and UV− vis analysis. 19,21,37 Herein, we exploited the double-imaging photoelectron photoion coincidence spectroscopy (i 2 PEPICO) to systematically analyze the production of formaldehyde in empty quartz and stainless steel reactors as well as over representative bed diluents and zeolite catalysts.…”

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

“…Interestingly, in the high-energy part of the Franck–Condon gap region between the B 1 B 2 and c 3 B 1 electronic states (between 16.2 and 16.7 eV binding energy), a weak signal from dissociation to the DL1 limit is also seen. This could indicate the presence of a conical intersection at long ON–O distances leading to internal conversion from the B 1 B 2 to lower lying states correlating to the DL1 limit, such as a 3 B 2 , b 3 A 2 , or A 1 A 2 …”

“…This could indicate the presence of a conical intersection at long ON−O distances leading to internal conversion from the B 1 B 2 to lower lying states correlating to the DL1 limit, such as a 3 B 2 , b 3 A 2 , or A 1 A 2 . 36 The dissociation of the c 3 B 1 and C 1 B 1 electronic states is also predominantly toward the DL2 limit, producing NO + (X 1 Σ + ) fragments with an average 1.6 eV kinetic energy release. The kinetic energy dissociated from the d 3 A 1 electronic state shows two components centered at ∼3.6 and 1.6 eV, corresponding to the dissociation toward the DL2 limit and the DL3 limit, respectively, as shown in Figure 5a, with the DL2:DL3 ratio changing as a function of electron binding energy.…”

Non-adiabatic Dynamics in a Continuous Circularly Polarized Laser Field with Floquet Phase-space Surface Hopping

“…Experiments have shown that strong monochromatic continuous wave (cw) light can change the landscape of potential energy surfaces and reaction channels by introducing light-induced states, or Floquet states in several different ways; e.g., there is now experimental evidence of light-induced conical intersections. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] During the past thirty years, various semiclassical formalisms for studying non-adiabatic phenomena have been demonstrated as effective and reasonably accurate. More recently, many surface hopping formalisms 20 have been generalized to incorporate time-dependent radiative couplings for light-induced non-adiabatic processes.…”