Skip to content

Exploring the energy disposal immediately after bond-breaking in solution: the wavelength-dependent excited state dissociation pathways of para-methylthiophenol

Research output: Contribution to journalArticle

Standard

Exploring the energy disposal immediately after bond-breaking in solution : the wavelength-dependent excited state dissociation pathways of para-methylthiophenol. / Zhang, Yuyuan; Oliver, Thomas A.A.; Das, Saptaparna; Roy, Anirban; Ashfold, Michael N. R.; Bradforth, Stephen E.

In: Journal of Physical Chemistry A, Vol. 117, No. 46, 03.10.2013, p. 12125-12137.

Research output: Contribution to journalArticle

Harvard

APA

Vancouver

Author

Zhang, Yuyuan ; Oliver, Thomas A.A. ; Das, Saptaparna ; Roy, Anirban ; Ashfold, Michael N. R. ; Bradforth, Stephen E. / Exploring the energy disposal immediately after bond-breaking in solution : the wavelength-dependent excited state dissociation pathways of para-methylthiophenol. In: Journal of Physical Chemistry A. 2013 ; Vol. 117, No. 46. pp. 12125-12137.

Bibtex

@article{26235dde938c4baeb7e70bf89710413c,
title = "Exploring the energy disposal immediately after bond-breaking in solution: the wavelength-dependent excited state dissociation pathways of para-methylthiophenol",
abstract = "A wavelength-resolved (λpump = 295, 285, 270, and 267 nm) photodissociation study of para-methylthiophenol (p-MePhSH) in ethanol solution has been performed using femtosecond transient absorption (TA) spectroscopy, and the results compared with those from studies of the corresponding photodissociation in cyclohexane solution at 270 nm. Anisotropy spectra are used to identify the electronic character of the initially populated excited state(s). S-H bond fission is found to occur via the dissociative S2(1(1)πσ*) state, which can be populated directly, or by ultrafast nonradiative transitions from the S3(2(1)ππ*) state, or by very efficient tunneling from the S1(1(1)ππ*) state, depending on the excitation wavelength, in line with conclusions from previous gas-phase studies of this same molecular photodissociation (Oliver, T. A. A.; King, G. A.; Tew, D. P.; Dixon R. N.; Ashfold, M. N. R. J. Phys. Chem. A 2012, 116, 12444). p-MePhS radicals are observed on a time scale faster than the instrument response at all wavelengths, but the available time resolution affords a rare opportunity to explore the branching between different electronic states of a product (the {\~A} and X̃ states of the p-MePhS radical in this case). The present study provides estimates of this branching in the products formed immediately after the first pass through the conical intersection (CI) between the S2 and S0 states. At 270 nm, for example, we identify a marked population inversion in the radical products, in contrast to the reported gas phase behavior. The finding that the contrast in branching ratio is largest between cyclohexane solution and the gas phase, with ethanol being intermediate, can be rationalized by recognizing the differing distributions of the S-H torsion angle (relative to the ring plane) in a room temperature solution compared with those in a jet-cooled molecular beam. The available time resolution also allows exploration of the electronic quenching of nascent {\~A} state radicals as solvent motion encourages recrossing of the S2/S0 CI. The average separation distance, , between the H + p-MePhS products arising in successful dissociation events is seen to increase with decreasing photolysis wavelength. This finding accords with the previous gas phase results, which determined that most of the excess energy following population of the dissociative S2 state (directly, or by ultrafast coupling from the S3 state) is released as product translation, and the expectation that should scale with the total kinetic energy release. The present work also confirms that geminate recombination of the H + p-MePhS products leads not just to reformation of parent p-MePhSH molecules but also to alternative adducts wherein the H atom bonds to the benzene ring. Analysis of the present data and results of high level ab initio calculations together with recent UV-IR pump-probe measurements (Murdock, D.; Harris, S. J.; Karsili, T. N. V.; Greetham, G. M.; Clark, I. P.; Towrie, M.; Orr-Ewing, A. J.; Ashfold, M. N. R. J. Phys. Chem. Lett. 2012, 3, 3715) allows identification of the likely adduct structures.",
keywords = "RESONANCE RAMAN, PHOTOFRAGMENTATION DYNAMICS, ABSORPTION-SPECTROSCOPY, FEMTOSECOND PHOTOLYSIS, SOLVATED ELECTRONS, LIQUID-PHASES, PHOTODISSOCIATION, MOLECULES, SPECTRA, WATER, CONICAL INTERSECTIONS, solution reaction dynamics, ultrafast photodissociation, radical recombination",
author = "Yuyuan Zhang and Oliver, {Thomas A.A.} and Saptaparna Das and Anirban Roy and Ashfold, {Michael N. R.} and Bradforth, {Stephen E.}",
year = "2013",
month = "10",
day = "3",
doi = "10.1021/jp405160n",
language = "English",
volume = "117",
pages = "12125--12137",
journal = "Journal of Physical Chemistry A",
issn = "1089-5639",
publisher = "American Chemical Society",
number = "46",

}

RIS - suitable for import to EndNote

TY - JOUR

T1 - Exploring the energy disposal immediately after bond-breaking in solution

T2 - the wavelength-dependent excited state dissociation pathways of para-methylthiophenol

AU - Zhang, Yuyuan

AU - Oliver, Thomas A.A.

AU - Das, Saptaparna

AU - Roy, Anirban

AU - Ashfold, Michael N. R.

AU - Bradforth, Stephen E.

PY - 2013/10/3

Y1 - 2013/10/3

N2 - A wavelength-resolved (λpump = 295, 285, 270, and 267 nm) photodissociation study of para-methylthiophenol (p-MePhSH) in ethanol solution has been performed using femtosecond transient absorption (TA) spectroscopy, and the results compared with those from studies of the corresponding photodissociation in cyclohexane solution at 270 nm. Anisotropy spectra are used to identify the electronic character of the initially populated excited state(s). S-H bond fission is found to occur via the dissociative S2(1(1)πσ*) state, which can be populated directly, or by ultrafast nonradiative transitions from the S3(2(1)ππ*) state, or by very efficient tunneling from the S1(1(1)ππ*) state, depending on the excitation wavelength, in line with conclusions from previous gas-phase studies of this same molecular photodissociation (Oliver, T. A. A.; King, G. A.; Tew, D. P.; Dixon R. N.; Ashfold, M. N. R. J. Phys. Chem. A 2012, 116, 12444). p-MePhS radicals are observed on a time scale faster than the instrument response at all wavelengths, but the available time resolution affords a rare opportunity to explore the branching between different electronic states of a product (the à and X̃ states of the p-MePhS radical in this case). The present study provides estimates of this branching in the products formed immediately after the first pass through the conical intersection (CI) between the S2 and S0 states. At 270 nm, for example, we identify a marked population inversion in the radical products, in contrast to the reported gas phase behavior. The finding that the contrast in branching ratio is largest between cyclohexane solution and the gas phase, with ethanol being intermediate, can be rationalized by recognizing the differing distributions of the S-H torsion angle (relative to the ring plane) in a room temperature solution compared with those in a jet-cooled molecular beam. The available time resolution also allows exploration of the electronic quenching of nascent à state radicals as solvent motion encourages recrossing of the S2/S0 CI. The average separation distance, , between the H + p-MePhS products arising in successful dissociation events is seen to increase with decreasing photolysis wavelength. This finding accords with the previous gas phase results, which determined that most of the excess energy following population of the dissociative S2 state (directly, or by ultrafast coupling from the S3 state) is released as product translation, and the expectation that should scale with the total kinetic energy release. The present work also confirms that geminate recombination of the H + p-MePhS products leads not just to reformation of parent p-MePhSH molecules but also to alternative adducts wherein the H atom bonds to the benzene ring. Analysis of the present data and results of high level ab initio calculations together with recent UV-IR pump-probe measurements (Murdock, D.; Harris, S. J.; Karsili, T. N. V.; Greetham, G. M.; Clark, I. P.; Towrie, M.; Orr-Ewing, A. J.; Ashfold, M. N. R. J. Phys. Chem. Lett. 2012, 3, 3715) allows identification of the likely adduct structures.

AB - A wavelength-resolved (λpump = 295, 285, 270, and 267 nm) photodissociation study of para-methylthiophenol (p-MePhSH) in ethanol solution has been performed using femtosecond transient absorption (TA) spectroscopy, and the results compared with those from studies of the corresponding photodissociation in cyclohexane solution at 270 nm. Anisotropy spectra are used to identify the electronic character of the initially populated excited state(s). S-H bond fission is found to occur via the dissociative S2(1(1)πσ*) state, which can be populated directly, or by ultrafast nonradiative transitions from the S3(2(1)ππ*) state, or by very efficient tunneling from the S1(1(1)ππ*) state, depending on the excitation wavelength, in line with conclusions from previous gas-phase studies of this same molecular photodissociation (Oliver, T. A. A.; King, G. A.; Tew, D. P.; Dixon R. N.; Ashfold, M. N. R. J. Phys. Chem. A 2012, 116, 12444). p-MePhS radicals are observed on a time scale faster than the instrument response at all wavelengths, but the available time resolution affords a rare opportunity to explore the branching between different electronic states of a product (the à and X̃ states of the p-MePhS radical in this case). The present study provides estimates of this branching in the products formed immediately after the first pass through the conical intersection (CI) between the S2 and S0 states. At 270 nm, for example, we identify a marked population inversion in the radical products, in contrast to the reported gas phase behavior. The finding that the contrast in branching ratio is largest between cyclohexane solution and the gas phase, with ethanol being intermediate, can be rationalized by recognizing the differing distributions of the S-H torsion angle (relative to the ring plane) in a room temperature solution compared with those in a jet-cooled molecular beam. The available time resolution also allows exploration of the electronic quenching of nascent à state radicals as solvent motion encourages recrossing of the S2/S0 CI. The average separation distance, , between the H + p-MePhS products arising in successful dissociation events is seen to increase with decreasing photolysis wavelength. This finding accords with the previous gas phase results, which determined that most of the excess energy following population of the dissociative S2 state (directly, or by ultrafast coupling from the S3 state) is released as product translation, and the expectation that should scale with the total kinetic energy release. The present work also confirms that geminate recombination of the H + p-MePhS products leads not just to reformation of parent p-MePhSH molecules but also to alternative adducts wherein the H atom bonds to the benzene ring. Analysis of the present data and results of high level ab initio calculations together with recent UV-IR pump-probe measurements (Murdock, D.; Harris, S. J.; Karsili, T. N. V.; Greetham, G. M.; Clark, I. P.; Towrie, M.; Orr-Ewing, A. J.; Ashfold, M. N. R. J. Phys. Chem. Lett. 2012, 3, 3715) allows identification of the likely adduct structures.

KW - RESONANCE RAMAN

KW - PHOTOFRAGMENTATION DYNAMICS

KW - ABSORPTION-SPECTROSCOPY

KW - FEMTOSECOND PHOTOLYSIS

KW - SOLVATED ELECTRONS

KW - LIQUID-PHASES

KW - PHOTODISSOCIATION

KW - MOLECULES

KW - SPECTRA

KW - WATER

KW - CONICAL INTERSECTIONS

KW - solution reaction dynamics

KW - ultrafast photodissociation

KW - radical recombination

U2 - 10.1021/jp405160n

DO - 10.1021/jp405160n

M3 - Article

C2 - 24047130

VL - 117

SP - 12125

EP - 12137

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 46

ER -