Spectroscopy and relaxation dynamics of photoexcited anisole and anisole-d3 molecules in a supersonic jet

The Journal of Chemical Physics

Iljina

et al. 2012

146

Time-resolved photoelectron imaging was used to investigate the dynamical evolution of the initially prepared S(1) (ππ*) excited state of phenol (hydroxybenzene), catechol (1,2-dihydroxybenzene), resorcinol (1,3-dihydroxybenzene), and hydroquinone (1,4-dihydroxybenzene) following excitation at 267 nm. Our analysis was supported by ab initio calculations at the coupled-cluster and CASSCF levels of theory. In all cases, we observe rapid (<1 ps) intramolecular vibrational redistribution on the S(1) potential surface. In catechol, the overall S(1) state lifetime was observed to be 12.1 ps, which is 1-2 orders of magnitude shorter than in the other three molecules studied. This may be attributed to differences in the H atom tunnelling rate under the barrier formed by a conical intersection between the S(1) state and the close lying S(2) (πσ*) state, which is dissociative along the O-H stretching coordinate. Further evidence of this S(1)/S(2) interaction is also seen in the time-dependent anisotropy of the photoelectron angular distributions we have observed. Our data analysis was assisted by a matrix inversion method for processing photoelectron images that is significantly faster than most other previously reported approaches and is extremely quick and easy to implement.

Section: B Short-time (<1 Ps) Dynamicssupporting

confidence: 71%

Time-resolved photoelectron imaging of excited state relaxation dynamics in phenol, catechol, resorcinol, and hydroquinone

Livingstone

The Journal of Chemical Physics

Iljina

et al. 2012

146

“…Sub-picosecond IVR processes have previously been reported in several aromatic systems 6,15,29,54,55 and in the present experiments we are 42150 cm À1 above the 1 L b origin 56 -considerably higher than experimentally determined IVR thresholds reported in other aromatic systems. 57,58 However, we have seen no evidence in our previous work that ultrafast IVR processes directly lead to any significant PAD evolution. 6,15,29,59 The B1 ps rise exhibited by b 2 between 0.30-0.70 eV (see Fig.…”

Section: Discussioncontrasting

confidence: 59%

Time-resolved photoionization spectroscopy of mixed Rydberg-valence states: indole case study

Zawadzki

Phys. Chem. Chem. Phys.

Burgess

et al. 2015

Time-resolved photoelectron imaging was used to study non-adiabatic relaxation dynamics in gas-phase indole following photo-excitation at 267 nm and 258 nm. Our data analysis was supported by various ab initio calculations using both coupled cluster and density functional methods. The highly differential energy- and angle-resolved information provided by our experimental approach provides extremely subtle details of the complex interactions occurring between several low-lying electronically excited states. In particular, new insight into the role and fate of the mixed Rydberg-valence 3s/πσ* state is revealed. This includes population residing on the excited state surface at large N-H separations for a relatively long period of time (∼1 ps) prior to dissociation and/or internal conversion. Our findings may, in part, be rationalized by considering the rapid evolution of this state's electronic character as the N-H stretching coordinate is extended - as extensively demonstrated in the supporting theory. Overall, our findings highlight a number of important general caveats regarding the nature of mixed Rydberg-valence excited states, their spectral signatures and detection sensitivity in photoionization measurements, and the evaluation of their overall importance in mediating electronic relaxation in a wide range of small model-chromophore systems providing bio-molecular analogues - a topic of considerable interest within the chemical dynamics community over the last decade.

“…24 In the experiments under discussion here, we are in excess of 6000 cm −1 above the S 1 (ππ * ) origin in all cases, which is considerably higher than the experimentally determined IVR onset threshold in the excited 1 (ππ * ) states of similar aromatic systems such as hydroquinone (1650 cm −1 ) and anisole (940 cm −1 ). 47,48 The ultimate fate of the S 1 (ππ * ) state is not resolved in our measurements but several possibilities suggested on the basis of previous work in aniline include fluorescence, 49 intersystem crossing to lower-lying triplet states, 50 and internal conversion back to the S 0 ground state, where the role played by prefulvene-like structures has attracted some recent attention. 12,14 Theoretical work by Fielding and co-workers predicts aniline has four CIs connecting the S 1 (ππ * ) and S 0 states, the lowest lying of which has a transition state located at ≥4.96 eV above the S 0 minimum energy.…”

Section: A τ 2 and τ 3 Decay Associated Spectramentioning

confidence: 88%

Ultraviolet relaxation dynamics of aniline, N, N-dimethylaniline and 3,5-dimethylaniline at 250 nm

The Journal of Chemical Physics

Saalbach

Crane

et al. 2015

Time-resolved photoelectron imaging was used to investigate the electronic relaxation dynamics of gas-phase aniline, N, N-dimethylaniline, and 3,5-dimethylaniline following ultraviolet excitation at 250 nm. Our analysis was supported by ab initio coupled-cluster calculations evaluating excited state energies and (in aniline) the evolution of a range of excited state physical properties as a function of N-H bond extension. Due to a lack of consistency between several earlier studies undertaken in aniline, the specific aim of this present work was to gain new insight into the previously proposed non-adiabatic coupling interaction between the two lowest lying singlet excited states S1(ππ(∗)) and S2(3s/πσ(∗)). The methyl-substituted systems N, N-dimethylaniline and 3,5-dimethylaniline were included in order to obtain more detailed dynamical information about the key internal molecular coordinates that drive the S1(ππ(∗))/S2(3s/πσ(∗)) coupling mechanism. Our findings suggest that in all three systems, both electronic states are directly populated during the initial excitation, with the S2(3s/πσ(∗)) state then potentially decaying via either direct dissociation along the N-X stretching coordinate (X = H or CH3) or internal conversion to the S1(ππ(∗)) state. In aniline and N, N-dimethylaniline, both pathways most likely compete in the depletion of S2(3s/πσ(∗)) state population. However, in 3,5-dimethylaniline, only the direct dissociation mechanism appears to be active. This is rationalized in terms of changes in the relative rates of the two decay pathways upon methylation of the aromatic ring system.