Time evolution studies of triplet toluene by two-color photoionization

Abstract

Rovibronically selected and resolved two-color laser photoionization and photoelectron study of cobalt carbide cation J. Chem. Phys. 138, 094301 (2013); 10.1063/1.4790707Rovibronically selected and resolved two-color laser photoionization and photoelectron study of nickel carbide cation J. Chem. Phys. 133, 054310 (2010); 10.1063/1.3464488Twocolor photoionization of naphthalene and benzene at threshold Two-color photoionization has been applied to measurement of the time evolution of laser-excited IB ,(mr*) vibronic levels of toluene, The observed photoionization signals exhibit a biexponential dependence upon the time delay between the pump and ionizing lasers, This photon intensity is shown to be proportional to the population of the excited singlet (SI) and triplet (Tt) electronic states, The data is fit to a simple kinetic model which yields the rates of S I fluorescent decay, S I Tt, and Tt v··SJ intersystem crossings. The measured quantum yield for intersystem crossing was found to agree with previous work. The triplet lifetimes measured are considerably shorter than values reported for collisionally relaxed triplet states due to the steep excess vibrational energy dependence of the nonradiative rate. This excess energy dependence of the triplet decay rate has been measured over a limited range of energy and the observed rates are found not to extrapolate smoothly to the decay rate measured for the vibrationless T I level. This behavior is rationalized as a dilution of excitation in good accepting modes for the T SJ transition due to increasing dominance of lower frequency, poor accepting modes in the triplet density of states.

H elimination and metastable lifetimes in the UV photoexcitation of diacetylene

“…This is the decay rate that represents the metastable lifetime for an isolated molecule, and one that we can measure by using a UV-pump, VUV-probe strategy. In this approach, analogous to early studies by Smalley and coworkers (25,26), the nanosecond UV laser excites C 4 H 2 , after which it relaxes rapidly to T 1 . A 7.9-eV (157 nm, F 2 excimer) probe laser can then ionize the electronically excited states of (27)], but not the ground state.…”

Photoelectron spectroscopy of S1 toluene: II. Intramolecular dynamics of selected vibrational levels in S1 toluene studied by nanosecond and picosecond time-resolved photoelectron spectroscopies

“…It is known that molecules such as toluene undergo slow intersystem crossing, and the intersystem crossing ͑ISC͒ lifetime for toluene has been measured as 0.19 s for S 1 v =0 at a rotational temperature of ϳ1 K. 10 It should be noted that the deduction of this lifetime assumes that the ionization cross section does not depend strongly on wavelength, an assumption that we have shown to be false in the case of the related molecule p-difluorobenzene. 33 We have investigated the possibility that the congestion observed in our photoelectron spectra arises from the photoionization of a vibrationally excited triplet state, T 1 * , by performing a nanosecond timeresolved two-color VMI experiment where the first photon is tuned to the S 1 ← S 0 origin and the wavelength of the second is 225 nm, judged to be short enough to efficiently ionize the triplet ͑i.e., to reach the Franck-Condon favored levels of the ion͒.…”

“…In the course of studies of the excited states of small aromatic molecules attention is often paid to issues such as intramolecular vibrational energy redistribution ͑IVR͒, [1][2][3][4][5][6][7][8] intersystem crossing and internal conversion, [9][10][11][12][13][14] torsional motion of side groups, 6,[15][16][17] and conformation. 18 Toluene in its first excited electronic state, S 1 , has been the subject of a number of extensive studies, 1,6 and is known to undergo intersystem crossing out of v =0, 10,13 and both internal conversion and IVR at higher levels of vibrational excitation.…”

“…18 Toluene in its first excited electronic state, S 1 , has been the subject of a number of extensive studies, 1,6 and is known to undergo intersystem crossing out of v =0, 10,13 and both internal conversion and IVR at higher levels of vibrational excitation. 1,14 Although rates are known in some instances, the photophysical properties of S 1 toluene have yet to be fully understood.…”

Electronic Spectroscopy of Toluene in Helium Nanodroplets: Evidence for a Long-Lived Excited State

“…Thus, if similar values apply for toluene in helium droplets, then ISC should be the major product channel following population of the S 1 state of the neutral molecule. 15 In the isolated molecule the zero point level of the lowest triplet state (T 1 ) lies 8400 cm -1 below that of the S 1 state and so ISC will convert this excess energy into vibrational 10 energy in the toluene. The molecule will most likely relax fully to the zero point level of the T 1 state on a relatively short timescale and evaporation of a minimum of 1680 helium atoms is expected if each helium atom removes 5 cm -1 of energy.…”