Quantum control of internal conversion in 24-vibrational-mode pyrazine

Abstract

Quantum control of the S(2)-->S(1) internal conversion in a complete 24-mode dimensionality model of pyrazine is demonstrated. The fully quantum mechanical study makes use of the recently developed "QP algorithm" for performing accurate computations of projected quantum dynamics and the role of overlapping resonances in control. The results are extremely encouraging, demonstrating active control over internal conversion so as to almost completely suppress the process over time scales of approximately 50-100 fs [well in excess of the natural internal conversion times (approximately 20 fs)] or to accelerate it to complete internal conversion in less than 5 fs. A number of new diagnostics are introduced to demonstrate the significance of overlapping-resonance contributions to control. Control is far better than for a reduced dimensionality model of pyrazine, presumably because of the increased degree of overlap between bound state resonances existing in the full dimensionality case.

Molecular response in one-photon absorption via natural thermal light vs. pulsed laser excitation

“…Consider, for example, natural thermal light incident on pyrazine. Here, the well-known excitation is from the S 0 electronic ground state to an S 2 excited state (36)(37)(38). This S 2 state is, in turn, coupled to an S 1 state, which will be occupied as the CW light drives the system into stationary states.…”

Active control of the lifetime of excited resonance states by means of laser pulses

“…[3][4][5][6][7][8][9][10] Several control targets have been pursued, among them control of the yield of specific molecular reaction pathways [4][5][6][7][8][9] and control of radiationless transitions and decoherence of initially excited molecular states. [11][12][13][14] This latter topic has potential applications in numerous fields, including quantum information processing and quantum computing. 15 One of the strategies proposed to control the survival of initially excited molecular states is based on the quantum interference effects that occur between overlapping zerothorder resonances of the system when a coherent superposition of such resonances is created.…”

“…15 One of the strategies proposed to control the survival of initially excited molecular states is based on the quantum interference effects that occur between overlapping zerothorder resonances of the system when a coherent superposition of such resonances is created. [12][13][14] By optimizing the coefficients of the different overlapping resonances in the superposition prepared (e.g., by means of pulse shaping), it is possible either to minimize or to maximize the lifetime of the initial superposition state, and this has been successfully achieved for a number of model systems. [12][13][14] The presence of overlapping resonances in a large variety of molecular systems makes this control scheme widely applicable.…”

Coherent phase control of internal conversion in pyrazine

“…This study focused on exploring a general phenomenon, and its treatment of the potential energy of pyrazine was highly simplified. In a related approach, Brumer, Shapiro, and coworkers [11,13,14] expressed the bright states of S 2 as linear combinations of eigenstates of the complete 24-mode coupled Hamiltonian. By choosing a suitable linear combination of overlapping resonances, they were able to suppress S 2 → S 1 internal conversion for periods of 50 − 100 fs.…”

“…[4] In still stronger fields, electrons are removed and subsequent chemistry takes place on a cationic surface. [5] The pyrazine molecule has been used as a benchmark case for many theoretical control schemes [6][7][8][9][10][11][12][13][14][15][16][17] as well as for experimental time-resolved studies of internal conversion (IC). [19][20][21] Reasons for interest in this molecule are its simple heterocyclic structure (C 4 N 2 H 4 ), symmetry (D 2h ), and small number of valence electrons.…”