Photoelectron-photofragment coincidence spectroscopy of the dissociative photodetachment of I2- at 258 and 266 nm

Relativistic four-component MRCISD+Q calculations of the six lowest valence states of molecular [Formula: see text] anion including breit interactions

CONTEXT AND RESULTS

This study aimed to obtain potential energy curves within a multireference 4-component relativistic method and to present spectroscopic constants (R[Formula: see text],[Formula: see text],[Formula: see text]x[Formula: see text],[Formula: see text]y[Formula: see text], D[Formula: see text], D[Formula: see text], B[Formula: see text],[Formula: see text],[Formula: see text],[Formula: see text] ), accurate extended Rydberg analytical form, and rovibrational levels for the 6 low-lying states of the I[Formula: see text] anion. For these states, some spectroscopic constants, rovibrational levels, and an accurate analytical form are presented for the first time in literature, and they are of interest for femtosecond and dynamics experiments of I[Formula: see text] as well as for electron attachment of I[Formula: see text]. This study suggests that the inclusion of relativistic and correlation effects treated at the MRCISD+Q level is needed to obtain reliable results, specially for D[Formula: see text].

COMPUTATIONAL AND THEORETICAL TECHNIQUES

The potential energy curves of the ground and the excited states of the molecular iodine anion (I[Formula: see text]) were investigated at multireference configuration interaction (MRCISD) with Davidson size-extensivity correction (denoted as +Q) within a fully relativistic four-component relativistic framework including Breit interaction.

Photoelectron photofragment coincidence spectroscopy of aromatic carboxylates: benzoate and p-coumarate

Photoelectron-photofragment coincidence spectroscopy was used to study the dissociation dynamics of the conjugate bases of benzoic acid and p-coumaric acid. Upon photodetachment at 266 nm (4.66 eV) both aromatic carboxylates undergo decarboxylation, as well as the formation of stable carboxyl radicals. The key energetics are computed using high-level electronic structure methods. The dissociation dynamics of benzoate were dominated by a two-body DPD channel resulting in CO₂ + C₆H₅ + e^-, with a very small amount of stable C₆H₅CO₂ showing that the radical ground state is stable and the excited states are dissociative. For p-coumarate (p-CA^-) the dominant channel is photodetachment resulting in a stable radical and a photoelectron with electron kinetic energy (eKE) <2 eV. We also observed a minor two-body dissociative photodetachment (DPD) channel resulting in CO₂ + HOC₆H₄CHCH + e^-, characterized by eKE <0.8 eV. Evidence was also found for a three-body ionic photodissociation channel producing HOC₆H₅ + HCC^- + CO₂. The ion beam contained both the phenolate and carboxylate isomers of p-CA^-, but DPD only occurred from the carboxylate form. For both species DPD is seen from the first and second excited states of the radical, where vibrational excitation is required for decarboxylation from the first excited radical state.

Photoelectron-photofragment coincidence spectroscopy of the mixed trihalides

Photoelectron-photofragment coincidence (PPC) spectroscopy is used to study the photodetachment, photodissociation, and dissociative photodetachment (DPD) of I₂Br^-, IBr₂ ^-, I₂Cl^-, and ICl₂ ^- at 266 nm. The mixed trihalides are asymmetric analogs of the well-studied I₃ ^- anion, with distinguishable dissociation asymptotes and the potential for selective bond breaking. The high beam energy PPC spectrometer used in this study couples an electrospray ionization source, a hexapole accumulation ion trap, and a linear accelerator to produce a 21 keV beam of a particular trihalide. Total, stable, and dissociative photoelectron spectra have been recorded for all the anions, except ICl₂ ^- that does not photodetach at 266 nm. A bound ground state (X) is observed for all the anions, and a dissociative first excited (A) state is also seen for I₂Br^- and I₂Cl^- at low electron kinetic energies (eKE). A 258 nm photoelectron spectrum recorded for I₂Br^- and I₂Cl^- rules out autodetachment of a dipole-bound state as the origin of the low eKE feature. The threshold detachment energy (TDE) of I₂X^- to the X state of the radical is similar to I₃ ^-, whereas the TDE to the radical A state increases with substitution of iodine for a lighter halogen. Two-body DPD is observed for I₂Br^- and I₂Cl^-, resulting in IBr/ICl + I + e^-. For IBr₂ ^- and ICl₂ ^-, the charge symmetric three-body photodissociation of [Br-I-Br]^- and [Cl-I-Cl]^- is seen yielding Br + Br and Br + Br^*, and Cl + Cl and Cl + Cl^* neutral fragments. Evidence for the minimum energy anion structure is observed in all cases, where the iodine atom is located at the center of the trihalide.