Luminescence and radiationless transitions from single vibronic levels of the isolated pyrazine molecule in the S 1(n,π*) state

Abstract

Luminescence spectra, fluorescence, and phosphorescence yields were measured for pyrazine excited to six different vibronic levels of the S 1(n,π*) state in pure pyrazine vapor and in gaseous pyrazine-SF6 mixtures. The vibrational analysis of the fluorescence spectrum is given. As the total gas pressure increases from 10−2 to several torr, the fluorescence yield decreases and reaches a constant pressure-independent value almost identical with that observed in condensed phases. The amount of this effect depends on the energy of the excited vibronic level. The phosphorescence yield, equal to zero at the low-pressure limit, increases with gas pressure. The deviation from the Stern-Volmer law for the fluorescence quenching is explained by the nonexponential decay of the fluorescence, evidenced by direct measurements of the decay curves. The results are discussed in terms of the kinetic and quantum-mechanical models of radiationless transitions in intermediate-size molecules.

Femtosecond time-resolved photoelectron imaging on ultrafast electronic dephasing in an isolated molecule

“…[1][2][3][4] It was predicted 2 that coherent excitation of an intermediate case molecule exhibits biexponential fluorescence decay I(t),…”

Femtosecond photoelectron imaging of pyridazine: S1 lifetime and (3s(n−1),3p(n−1)) Rydberg state energetics

“…[7][8][9][10][11][12] In particular, pyrazine is the beststudied molecule of an intermediate case, 7,8,10,11 and it is well accepted now that the optically prepared S 1 pyrazine dephases into T 1 manifolds with a lifetime of ϳ110 ps. Our previous study on pyrazine by time-resolved photoelectron imaging has firmly established this dynamics by visualizing both the decay of S 1 and buildup of T 1 characters in real time.…”

An explanation of the highly efficient magnetic quenching of fluorescence in intermediate case molecules based on two manifold models

“…The first sum represents the population decays of individual eigenstates ͑incoherent contribution͒ and the second one represents the s-character interference among eigenstates ͑coherent contribution͒. 29,30,34,35 The coherent excitation over the bandwidth ⌬E results in a rapid phase collapse ͑''dephasing''͒ among the eigenstates excited. The dephasing at early times (tϽប/⌬E) is purely exponential if the s-character distribution function ͑absorption profile͒ is a Lorentzian, that is, for the case of equally spaced, equally coupled ͉b j ͘ levels ͑the so-called Bixon-Jortner model͒.…”

“…The slow decay after tϾប/⌬E thus comes mainly from the sum of incoherent decays of individual eigenstates. 34,35 The energy levels for a set of independent oscillators ͑integrable system͒ are independently distributed in the energy axis. A collection of those levels will have many levels close or overlapping.…”