Direct observation of spin-forbidden transitions through the use of suitably polarized light

Abstract

The study of excited triplet states of a molecular system is a difficult task because accessing them involves forbidden transitions from the singlet ground state. Nevertheless, absorption spectra of many molecules present, at low energies, the weak fingerprint of these triplet states. At higher energies this information is usually masked by the intense signal of the singlet states. Here we show, for the specific case of the sulphur dioxide molecule, that the combined use of polarized light and molecular alignment can enhance the triplet part of the spectrum, even making it the only absorption process.

Excited state dynamics in SO2. III. An ab initio quantum study of single- and multi-photon ionization

“…One should note that the question of the triplet states and their role in the dynamics have not been investigated in the present work, but are highlighted by the second companion paper (Paper II) 48 using semi-classical methods. We would like to stress out that we have recently performed a full ab initio study of the three lowest triplet states of SO 2 , where we elucidated the triplet part of the photoabsorption spectrum 49 and the intersystem crossing. 50…”

Communication: Theoretical prediction of the importance of the 3B2 state in the dynamics of sulfur dioxide

“…The second description [23] uses quantum dynamics for the intersystem crossing between the former singlet states and only two triplet states ( 3 B 1 and 3 A 2 ) and gives rise to similar transfer, but in 1ps with only ~10% reached in 200fs. In this study, the authors committed two mistakes and two crude approximations (see [24]) by first discarding the 3 B 2 state and by wrongly introducing spin-orbit coupling (SOC) between the 3 B 1 ,and 1 B 1 states, and further by ignoring the conical intersection between the remaining triplet states and considering constant SOC.…”

Dynamical distortions of structural signatures in molecular high-order harmonic spectroscopy

“…Its position has long been ascribed to the zeros of the recombination dipole matrix element d rec given by Eq. (16), which relies on plane-waves (PW) to describe the continuum and on the LCAO approximation for the ground state [65]. Within these approximations, the zeros of d rec occur at particular momentum values p k = (2k + 1)π/R, k ∈ Z.…”