Discrete-continuum interactions and lineshapes in the autoionization spectra of BH Frauke Schroeder and Edward R. Grant Department of Chemistry University of British Columbia Vancouver Andrew T. Gilkison and C. Ricardo Viteri Purdue University West Lafayette 61st International Symposium on Molecular Spectroscopy Ohio June 19 – 23 2006

Motivation Few experiments on super excited states of molecules Dynamics of autoionization Characterization of continuum BH: simple six electron system model for new computational techniques Intricate web of potential energy surfaces Probing Rydberg series converging to BH+  potential of BH+ X 2+ state  potential energy surface of gateway state

Experiment (I): Laser excitation scheme 3 Dye laser FL2001 (ArF, 193 nm) COMPEX Excimer Excimer EMG 202 (XeCl, 308 nm) 2 BBO doubler Dye laser FL3002 skimmer Turbo- pumped vacuum chamber nozzle 1,2,3 linewidths  0.25 cm-1 5% B2H6 in 3 atm H2 1 OPO Panther Nd:YAG PL8000 (355 nm)

Experiment (II): Timing and ion detection preamp (gain = 10) scope sample and photolysis 1.5 ms later: excitation 50 ns later: +400 V pulse ion signal amplified and digitally recorded MCP PC (Labview) TOF-MS Extractor grid gas flow Repeller grid photolysis laser excitation lasers pulser (+400 V)

Excitation Routes v+ v+ + 1 w3 w2 w1

Rydberg Formula Approximate estimation of energy positions: BH+ X 2+ IP electronic energy levels Approximate estimation of energy positions: BH+ X 2+

Vibrational autoionization spectra

Third Photon Excitation V+=V’+1 V’ V+=V’-1 V+=V’ B 1+ X 2+ below threshold

Vibrational autoionization spectra

Third Photon Excitation V+=V’+1 V’ V+=V’-1 V+=V’ B 1+ X 2+ below threshold above threshold

Vibrational autoionization spectra

Fano Formalism Discrete state embedded in an underlying continuum are analyzed by the Fano formalism: ER q = 2 q =  q = 0 q = -2 and Intensity [a.u.] E [cm-1]

Analysis of experimental results Discrete state embedded in an underlying continuum are analyzed by the Fano formalism: and  Analysis of the spectra with respect to this formulism provides values for  and q.

Overall trends in line shapes Below threshold Above threshold  decreases with increasing n  increases with increasing v+ no significant change in magnitude

Overall trends in line shapes Below threshold Above threshold q increases with increasing n change in magnitude except for v+ = 2 but: change in sign from below to above threshold!!!

Line shapes below and above threshold BH+ X 2+ v+ = 2 from BH B 1+ v‘ = 2 BH+ X 2+ v+ = 2 from BH B 1+ v‘ = 1

Line shapes in terms of Fano formalism Discrete state embedded in an underlying continuum are analyzed by the Fano formalism: and where: and

Franck-Condon Factors Estimation of Franck-Condon Factors possible from equations for q Assumption: V is calculated from experimental linewidths: …analog for qabove v+ v‘ 1 2 3 4 0.90 0.18 -0.30 0.67 0.60 -0.61 0.54 -0.39 0.46 0.72

Contribution of Franck-Condon factors to q v+ below above 1 -2.23 0.20 2 -0.88 0.88 3 -1.19 1.00 4 1.56

Franck-Condon Factors v+ v‘ 1 2 3 4 0.90 0.18 -0.30 0.67 0.60 -0.61 0.54 -0.39 0.46 0.72

Interloper 7s (N+ = 1) 8p (N+ = 0; v+=4) 6s (N+ = 1; v+=6) 6p (N+ = 2)

Conclusions Triple resonance spectroscopy isolates high-Rydberg states of BH converging to v+ = 1 - 4. Lineshapes are well characterized by Fano formalism. Trends are explained: (v), sign of q, window resonances, etc. 2 v+ v‘ 1 3 4 0.8985 0.1820 -0.3015 0.6737 0.5953 -0.6121 0.5408 0.5433 -0.3889 0.4640 0.7229 Estimated Franck-Condon factors show higher values for off-diagonal elements for v‘ and v+ > 1. Interlopers indicate large interactions between vibrational series and huge differences in electronic potentials B of BH and X of BH+.

Acknowledgments Thank you for your attention! Prof. Edward Grant C. Ricardo Viteri Thank you for your attention!

Next:. Dynamics of dissociative recombination,. electron loss and Next: Dynamics of dissociative recombination, electron loss and isolated-core photon absorption in single rovibronic Rydberg resonances of 11BH C. Ricardo Viteri and Andrew T. Gilkison Department of Chemistry Purdue University West Lafayette Scott J. Rixon and Edward R. Grant University of British Columbia Vancouver 61st International Symposium on Molecular Spectroscopy Ohio June 19 – 23 2006