Evidencing an elusive conical intersection in the dissociative photoionization of methyl iodide.

The valence-shell dissociative photoionization of methyl iodide (CHI) is studied using double imaging photoelectron photoion coincidence (i PEPICO) spectroscopy in combination with highly-tunable synchrotron radiation from synchrotron SOLEIL. The experimental results are complemented by new high-level calculations of the potential energy curves of the relevant electronic states of the methyl iodide cation (CHI). An elusive conical intersection is found to mediate internal conversion from the initially populated first excited state, CHI(), into the ground cationic state, leading to the formation of methyl ions (CH).

Imaging the photodissociation dynamics of internally excited ethyl radicals from high Rydberg states.

The site-specific hydrogen-atom elimination mechanism previously reported for photoexcited ethyl radicals (CHCH) [D. V. Chicharro , , 2019, , 6494] is interrogated in the photodissociation of the ethyl isotopologues CDCD, CHCD and CDCH through the velocity map imaging (VMI) detection of the produced hydrogen- and deuterium-atoms.

Conical intersection and coherent vibrational dynamics in alkyl iodides captured by attosecond transient absorption spectroscopy.

The photodissociation dynamics of alkyl iodides along the C-I bond are captured by attosecond extreme-ultraviolet (XUV) transient absorption spectroscopy employing resonant ∼20 fs UV pump pulses. The methodology of previous experiments on CHI [Chang et al., J.

Mapping wave packet bifurcation at a conical intersection in CHI by attosecond XUV transient absorption spectroscopy.

Extreme ultraviolet (XUV) transient absorption spectroscopy has emerged as a sensitive tool for mapping the real-time structural and electronic evolution of molecules. Here, attosecond XUV transient absorption is used to track dynamics in the A-band of methyl iodide (CHI). Gaseous CHI molecules are excited to the A-band by a UV pump (277 nm, ∼20 fs) and probed by attosecond XUV pulses targeting iodine I(4d) core-to-valence transitions.

Revealing electronic state-switching at conical intersections in alkyl iodides by ultrafast XUV transient absorption spectroscopy.

Conical intersections between electronic states often dictate the chemistry of photoexcited molecules. Recently developed sources of ultrashort extreme ultraviolet (XUV) pulses tuned to element-specific transitions in molecules allow for the unambiguous detection of electronic state-switching at a conical intersection. Here, the fragmentation of photoexcited iso-propyl iodide and tert-butyl iodide molecules (i-CHI and t-CHI) through a conical intersection between Q/Q spin-orbit states is revealed by ultrafast XUV transient absorption measuring iodine 4d core-to-valence transitions.

Site-specific hydrogen-atom elimination in photoexcited ethyl radical.

The photochemistry of the ethyl radical following excitation to the 3p Rydberg state is investigated in a joint experimental and theoretical study. Velocity map images for hydrogen atoms detected from photoexcited isotopologues CHCH, CHCD and CDCH at ∼201 nm, are discussed along with high-level electronic structure calculations of potential energy curves and non-adiabatic coupling matrix elements (NACME). A novel mechanism governed by a conical intersection allowing prompt site-specific hydrogen-atom elimination is presented and discussed.

Threshold photoelectron spectrum of the CHOO Criegee intermediate.

We present the photoelectron spectroscopy of the simplest Criegee intermediate, CHOO, close to the first ionization energy. Comparison with existing theoretical data yields the experimental adiabatic ionization energy and provides a benchmark for theoretical studies on larger Criegee intermediates, which play an important role in the ozonolysis of alkenes.

A velocity-map imaging study of methyl non-resonant multiphoton ionization from the photodissociation of CHI in the A-band.

Chemical reaction dynamics and, particularly, photodissociation in the gas phase are generally studied using pump-probe schemes where a first laser pulse induces the process under study and a second one detects the produced fragments. Providing an efficient detection of ro-vibrationally state-selected photofragments, the resonance enhanced multiphoton ionization (REMPI) technique is, without question, the most popular approach used for the probe step, while non-resonant multiphoton ionization (NRMPI) detection of the products is scarce. The main goal of this work is to test the sensitivity of the NRMPI technique to fragment vibrational distributions arising from molecular photodissociation processes.