Measurement of hyperfine polarization quantum beats in a polyatomic molecule

Abstract

Polarization quantum beats between hyperfine components of perturbed rotational states in the S1→S0 fluorescence of propynal (HC≡CCHO) have been measured. The quantum beats are explained by a periodic transfer of molecular alignment to nuclear spin polarization.

Theory for determining alignment parameters of symmetric top molecule using (n+1) LIF

“…When a product molecule has a nonzero nuclear or electronic spin, the degree of rotational orientation or alignment may be altered to varying degrees by coupling the rotational angular momentum J to the nuclear spin I or electronic spin S of the molecule to form a resultant F. 26,27,40,46 The depolarization effects are observable at a low J quantum number. The depolarization effects induced by nuclear and electronic spins can be treated by using the angular momentum coupling theory and the Wigner-Eckart theorem.…”

“…The depolarization effects induced by nuclear and electronic spins can be treated by using the angular momentum coupling theory and the Wigner-Eckart theorem. Huber and co-workers 24,46 discussed the depolarization effect caused by the nuclear spins and derived the expressions for calculating the total state multipoles in the coupled representation of the molecular rotational angular momentum J and the nuclear spin I. Zare and co-workers 26-29 studied the depolarization effect induced by the nuclear spins in detail and derived a useful formula for calculating depolarization factor. For a symmetric top molecule with nuclear spins I, each state multipole l 0 Ϯ (L 0 ) (⌫ 0 ,⌫ 0 ) in Eqs.…”

Hyperfine quantum beats in the 209 nm fluorescence excitation spectrum of cyanogen

“…The fluorescence intensity following excitation with a linearly polarized laser pulse may be written as 3,10,13,14 I͑t,J i ,J e ,J f ͒ϰ͉͗J i ʈDʈJ e ͉͘ 2 ͉͗J e ʈDʈJ f ͉͘ 2 ϫ͑Ϫ1 ͒ J i ϩJ e ϩJ f ϩJ e ͚ kϭ0,2 ͑ 2kϩ1 ͒ ϫ ͩ 1 1 k 0 0 0 ͪ 2 ͭ 1 1 k J e J e J i ͮ ϫ ͭ 1 1 k J e J e J f ͮ P k ͑cos ͒G k ͑ t ͒, ͑A1͒…”

“…For comparison with experiment, it is convenient to sum Eq. ͑A3͒ over final state quantum numbers J f and rewrite the result in the form 3 :…”

“…2,9 Hyperfine quantum beats in both cyanogen and propynal are accurately described with a first-order perturbation theory two-state coupling model. Polarization quantum beat spectroscopy, 3 described with the Fano-Macek formulation, provides an elegant means for studies of the collisional relaxation of scalar, vector, and tensor fluorescence components. 8 In cyanogen, symmetry restrictions for the exchange of N 14 nuclei provide the basis for the selective excitation of states with either odd (Iϭ1) or even (Iϭ0,2) nuclear spin quantum numbers.…”