Field optimized initial state based control of photodissociation

A simplification of selective control using field optimized initial state with application to HI and IBr photodissociation

“…Earlier control schemes [8][9][10][11][12][13][14] have attempted control over photodissociation entirely through field design for a fixed (0). In the FOIST scheme, control over product yield is sought through preparation of the initial wave function (0) as a coherent superposition of vibrational eigenstates of the ground electronic state for the chosen photolysis pulse [22][23][24][25][26][27] ͑for the short femtosecond pulses to be considered here, rotational motion is ignored͒. Of course, the field itself may also be altered which will change the nature of the optimal (0).…”

“…The critical role played by the initial vibrational state of the molecule in the product selectivity and yield has motivated our development of a field optimized initial state ͑FOIST͒-based approach to the control of photodissociation reactions. [22][23][24][25][26][27] In this FOIST-based procedure, the control of photodissociation reactions is through the design of an optimal linear combination of a few selected vibrational states prior to the application of the photolysis pulse whose attributes may be chosen for ease of experimental realization. The optimal linear combination from the FOIST procedure achieves selective flux maximization by mixing excited vibrational states to suitably alter the spatial profile of the initial state to facilitate Franck-Condon transition to appropriate region of the excited electronic state͑s͒.…”

“…These optimal linear combinations are field and channel specific and analysis of the FOIST scheme for IBr and HI molecules has been presented earlier. [22][23][24][25][26][27] Initial applications of the FOIST scheme have however utilized a linear combination of the ground and first two excited vibrational states (vϭ0, 1, and 2, respectively͒ requiring a complex fundamental plus overtone excitation, making the experimental realization of these optimal initial states somewhat difficult. Also, the photolysis field ⑀(t) ϭA ͚ pϭ0 2 cos(Ϫ p,0 )t with ប p,0 ϭE p ϪE 0 utilized in these initial applications consists of a principal frequency and another two colors separated by vibrational frequency difference between vϭ0 (E 0 ) and vϭ1 (E 1 ) and vϭ0 and v ϭ2 (E 2 ).…”

“…The additional frequencies Ϫ 10 and Ϫ 20 provide for molecules in the vibrational levels vϭ1 and v ϭ2 to be transferred to the same final state as those in v ϭ0 under the influence of radiation with frequency . This permits a coherent interference between these different paths to the same final state enhancing selectivity and yield, [22][23][24][25][26][27] but the need for a multicolor photolysis field also adds to the complication of the FOIST scheme. The range of field parameters sampled in these initial applications [22][23][24][25][26][27] has also been somewhat limited.…”

“…It is therefore desirable to investigate, if over some range of frequencies, for a single color photolysis field of moderate intensity, an optimal superposition utilizing only the ground vibrational state (vϭ0) requiring no vibrational excitation or vϭ0 and vϭ1 vibrational states, requiring only the fundamental vibrational excitation for its experimental actuation, which can provide adequate selectivity and yield. Towards this end, it is our purpose in this article to map the dependence of flux in competing channels on vϭ0, vϭ1 and v ϭ2 initial vibrational states for the three color photolysis fields employed in earlier FOIST applications [22][23][24][25][26][27] as also for a two color ͓⑀(t)ϭA ͚ pϭ0 1 cos(Ϫ p,0 t)͔ and single color ͓⑀(t)ϭA cos t͔ simplifications thereof to try and identify the field parameters which will make possible a simpler experimental realization of selective photodynamic control. A probe of the underlying simplifying principles which can be a͒ CSIR senior research fellow.…”