On the Mechanism of Magnetic Quenching of Fluorescence in Gaseous State

Abstract

SummaryThe pressure dependence of fluorescence quenching of gaseous glyoxal has been measured in the presence of a magnetic field of 1-8 kG. Below 5 kG both the collision free lifetime and the collisional quenching constant were found to be dependent upon magnetic field strength. Above 5 kG the collisional quenching constant turned out to be nearly equal to the value without magnetic field and the collision free lifetime took a constant value larger than that without magnetic field.The magnetic enhancement of the intramolecular radiationless transition of gaseous molecules has been studied theoretically. The phenomenon is shown to be explained by considering two mechanisms, mechanisms I and 11. Mechanism I is due to the interaction of a primary state with secondary states through the Zeeman hamiltonian. Mechanism I1 is due to the shift and broadening of appropriate rovibronic levels by the Zeeman effect.

Rotational analysis of some vibronic bands in the 3A u←1A g transition of glyoxal. Spin splittings in the lowest triplet state of the isolated molecule

“…4 ,5 The structures and dynamic properties of several weakly bound van der Waals complexes of SI glyoxal have also been explored. 6 Singlet-triplet interactions in glyoxal have been studied using a variety of techniques including collision-induced ISC, 7 magnetic-field dependence of the fluorescence decay, 8 and level anticrossing experiments. 9 These results all refer to high-lying triplet rovibronic levels, isoenergetic (or nearly so) with rovibronic levels of the SI state.…”

Magnetic Field Influence on Dynamics of Singlet‐Triplet Conversion

“…Matrix elements of the Zeeman operator have been considered in publications [22,23,39,1161 where the angular momenta coupling schemes were analyzed for the case (a) after Hund, and also in the so-called "low"-and "high"-field limits of the case (b) after Hund. To analyze this problem, we have to note that the nonlinear polyatomic molecules belong to the Hund case (b) angular momenta coupling scheme; that is, their fine splitting energy of the triplet-state levels is much smaller than the energy interval between the rotational levels of the triplet vibronic state.…”

“…The observed effects were explained using the level anticrossing (LAM), direct (DM), and indirect (electron-spin and nuclear-spin decoupling) (IM) mechanism theories [19-231. Later we shall discuss these mechanisms in detail; here, however, we have to explain the meaning of terms DM and IM, because the frequently used definition of these mechanisms [21,22] differs from the one used here. In the literature, DM corresponds to a direct magnetic-field-induced coupling of the discrete levels of the fluorescent state with dissociative continuum or rovibronic quasi-continuum of the neighboring "dark" nonemitting state, while IM describes such coupling between the discrete levels of both the fluorescent and the "dark" states [21,22]. In both cases mentioned, the magnetic-field-induced interaction couples the fluorescent-state level with the dark-state levels in the first order of the perturbation theory.…”

“…For the Hund case (a), the matrix elements of the DAY(<{. 8. cp) operator are defined[22,23, 1161. Thus, the matrix elements required may be written as (-l)"-P ' [(2J + 1)(2J' respective selection rules for the matrix elements of the Hund case (Note that the orbital part of the Zeeman operator can mix different electronic states, while its spin part can mix levels of the same vibronic state only at S # 0.…”

Optical-IR double resonance effect for the rovibronic state of (COF)2

“…It has been found that in the presence of both magnetic and microwave fields, the (COF) 2 fluorescence intensity is reduced. The experimental results were explained using the indirect mechanism (IM) theory, employing the electron-spin and nuclear-spin decoupling mechanism (ESNSDM) [6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”