Vacuum Ultraviolet Excited State Dynamics of the Smallest Ketone: Acetone.

We combined tunable vacuum-ultraviolet time-resolved photoelectron spectroscopy (VUV-TRPES) with high-level quantum dynamics simulations to disentangle multistate Rydberg-valence dynamics in acetone. A femtosecond 8.09 eV pump pulse was tuned to the sharp origin of the A(n3d) band.

Vacuum ultraviolet excited state dynamics of small amides.

Time-resolved photoelectron spectroscopy in combination with ab initio quantum chemistry calculations was used to study ultrafast excited state dynamics in formamide (FOR), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA) following 160 nm excitation. The particular focus was on internal conversion processes within the excited state Rydberg manifold and on how this behavior in amides compared with previous observations in small amines. All three amides exhibited extremely rapid (<100 fs) evolution from the Franck-Condon region.

The influence of relativistic effects on nuclear magnetic resonance spin-spin coupling constant polarizabilities of H O , H S , H Se , and H Te.

Relativistic and nonrelativistic calculations have been performed on hydrogen peroxide, dihydrogen disulfide, dihydrogen diselenide, and dihydrogen ditelluride, H X (X = O, S, Se, Te), to investigate the consequences of relativistic effects on their structures as well as their nuclear magnetic resonance (NMR) spin-spin coupling constants and spin-spin coupling constant polarizabilites. The study has been performed using both one-component nonrelativistic and four-component relativistic calculations at the density functional theory (DFT) level with the B3LYP exchange-correlation functional. The calculation of nuclear spin-spin coupling constant polarizabilities has been performed by evaluating the components of the third order tensor, nuclear spin-spin coupling polarizability, using quadratic response theory.

Symmetry controlled excited state dynamics.

Symmetry effects in internal conversion are studied by means of two isomeric cyclic tertiary aliphatic amines in a velocity map imaging (VMI) experiment on the femtosecond timescale. It is demonstrated that there is a delicate structural dependence on when coherence is preserved after the transition between the 3p and 3s Rydberg states. N-Methyl morpholine (NMM) shows unambiguous preserved coherence, consistent with previous work, which is decidedly switched off by the repositioning of oxygen within the ring.

Vacuum ultraviolet excited state dynamics of the smallest ring, cyclopropane. II. Time-resolved photoelectron spectroscopy and dynamics.

The vacuum-ultraviolet photoinduced dynamics of cyclopropane (CH) were studied using time-resolved photoelectron spectroscopy (TRPES) in conjunction with quantum dynamics simulations. Following excitation at 160.8 nm, and subsequent probing via photoionization at 266.

Putting the Disulfide Bridge at Risk: How UV-C Radiation Leads to Ultrafast Rupture of the S-S Bond.

We investigate the ultrafast photoinduced dynamics of the cyclic disulfide 1,2-dithiane upon 200 nm excitation by time-resolved photoelectron spectroscopy and show that the S-S bond breaks on an ultrafast time scale. This stands in stark contrast to excitation at longer wavelengths where the initially excited S state evolves as the wavepacket is guided towards a conical intersection with S by a torsional motion involving a partially broken bond between the sulfur atoms. This process at lower excitation energy allows for efficient (re-)population of S , rendering dithiane intact.

Conformationally controlled ultrafast intersystem crossing in bithiophene systems.

Bithiophenes serve as model systems for larger polythiophenes used in solar cell applications and molecular electronics. We report a study of ultrafast dynamics of two bithiophene systems measured with femtosecond time-resolved photoelectron spectroscopy, and show that their intersystem crossing takes place within the first few picoseconds after excitation, in line with previous studies. We show that the intersystem crossing rate can be explained in terms of arguments based on symmetry of the S1 minimum energy geometry, which depends on the specific conformation of bithiophene.

Transient IR Spectroscopic Observation of Singlet and Triplet States of 2-Nitrofluorene: Revisiting the Photophysics of Nitroaromatics.

The dynamics of 2-nitrofluorene (2-NF) in deuterated acetonitrile is studied using UV pump, IR probe femtosecond transient absorption spectroscopy. Upon excitation to the vibrationally excited S1 state, the excited-state population of 2-NF branches into two different relaxation pathways. One route leads to intersystem crossing (ISC) to the triplet manifold within a few hundred femtoseconds and the other to internal conversion (IC) to the ground state.