Evidence for Perturbations in Acetylene S 1 Levels from Stimulated Emission Pumping (SEP) Spectra A Coy Wink from the cis-Well? Barratt Park, Joshua H. Baraban, Adam H. Steeves, Robert W. Field Massachusetts Institute of Technology OSU International Symposium on Molecular Spectroscopy Tuesday, June 21, 2011

Stimulated Emission Pumping Provides FC Access to Vibrationally-Excited S 0 S0S0 S1S1 Energy Bending Coordinate cm cm -1 H-CCH D cm -1 0 cm cm cm cm -1

Evidence for cis-trans interaction in DF spectra from 6 3 ’ Two overlapping bands were assigned to 6 3 ’ and “U” (containing 6 ’) on the basis of DF spectra. K. Tsuji, C. Terauchi, K. Shibuya, S. Tsuchiya, Chem. Phys. Lett. 306 (1999) 41-47

Evidence for cis-trans interaction in DF spectra from 6 3 ’ 6 3 ’ DF features progressions in 2 ” and 4 ”. DF from “U” displays shifts in peaks of 4 ” progressions. Appears to feature progressions in 2 5 ” and 2 ”. Anomalous Franck-Condon activity from 6 3 ’ above 10,000 cm -1 may arise from mixing with “U”. Strong FC-forbidden 4 ’ + 6 ’ character is explained in terms of anharmonic resonance mediated by the cis-trans barrier. K. Tsuji, C. Terauchi, K. Shibuya, S. Tsuchiya, Chem. Phys. Lett. 306 (1999) Dispersed Fluorescence 4 3 ’ 5 3 ’ 6 3 ’ “U”

Evidence for cis-trans interaction in DF spectra from 6 3 ’ 6 3 ’ DF features progressions in 2 ” and 4 ”. DF from “U” displays shifts in peaks of 4 ” progressions. Appears to feature progressions in 2 5 ” and 2 ”. Anomalous Franck-Condon activity from 6 3 ’ above 10,000 cm -1 may arise from mixing with “U”. Strong FC-forbidden 4 ’ + 6 ’ character is explained in terms of anharmonic resonance mediated by the cis-trans barrier. K. Tsuji, C. Terauchi, K. Shibuya, S. Tsuchiya, Chem. Phys. Lett. 306 (1999) cm -1 = 2 5 ” 1850 cm -1 = 2 ” 4 3 ’ 5 3 ’ 6 3 ’ “U” Dispersed Fluorescence

Transitions Obey Strict FC Propensities A g 3040 cm -1 1 ’ A g 1386 cm -1 2 ’ A g 1047 cm -1 3 ’ A u 764 cm -1 4 ’ B u 2857 cm -1 5 ’ B u 768 cm -1 6 ’  g cm -1 1 ”  g cm -1 2 ”  u cm -1 3 ”  u 727 cm -1 5 ”  g 612 cm -1 4 ” FC active “ B ’”

“One Bright State Per Polyad” “FC active” modes on S 0 are 2 ’’ (CC stretch) and 4 ’’ (trans-bend). Conserved Polyad numbers on S 0 are By inspection, there is only one combination of v 2 ” and v 4 ” that conserve these numbers in a given polyad (v 1 ”, v 3 ”, v 5 ” held constant). Intra-polyad interactions can slosh around the brightness from this combination of 2 ’’ and 4 ’’ to the polyad eigenstates, but spectra from most “normal” S 1 levels will light up only one zero-order bright state. Exception: Excitation in B ’ ( 4 ’ and 6 ’) will light up multiple ZOBS differing in ℓ 4, ℓ 5.

SEP to Pure Bending Polyad N B ” = 10 “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump Q(1) (III) Q(1) (II) R(1) (I) Internal Energy/cm -1 SEP Intensity Internal Energy/cm -1 Simulation of J”=1, ℓ 4 =ℓ 5 =0, N B ”=10 ZOBS SEP 2 3 ’ 2 B ’ Polyad

SEP to Pure Bending Polyad N B ” = 10 Q(1) (III) Q(1) (II) R(1) (I) Internal Energy/cm -1 SEP Intensity Internal Energy/cm -1 SEP “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump [10 0, 0 0 ] [10 2, 0 0 ] Simulated Spectrum “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump 2 3 ’ 2 B ’ Polyad

SEP to Pure Bending Polyad N B ” = ’ 2 B ’ Polyad Q(1) (III) Q(1) (II) R(1) (I) Internal Energy/cm -1 SEP Intensity Internal Energy/cm -1 SEP 0.49[8 0, 2 0 ]-0.87[8 2, 2 -2 ] 0.92[8 0, 2 2 ]+0.33[8 4, 2 -2 ]+0.22[8 2, 2 0 ] “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump 2 3 ’ 2 B ’ Polyad Q(1) (III) [8 0, 2 0 ] [8 2, 2 -2 ] [8 0, 2 2 ] [8 4, 2 -2 ] [8 2, 2 0 ] g-g-

Anomalous SEP from 4 3 ’ Does not Match “Normal” ZOBS Pattern 2 3 ’ 2 B ’ Polyad Q(1) (III) Q(1) (II) R(1) (I) Internal Energy/cm -1 SEP Intensity “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump 4 3 ’

Q(1) (III) Q(1) (II) R(1) (I) Internal Energy/cm -1 SEP Intensity “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump 4 3 ’ near-perfect interference? “[8 0, 2 0 ]” “[6 4, 4 -4 ]” “[6 2, 4 -2 ]” “[8 2, 2 0 ]” Anomalous SEP from 4 3 ’ Does not Match “Normal” ZOBS Pattern 2 3 ’ 2 B ’ Polyad

Q(1) (III) Q(1) (II) R(1) (I) Internal Energy/cm -1 SEP Intensity “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump 4 3 ’ Extra Feature “[6 4, 4 -4 ]” Anomalous SEP from 4 3 ’ Does not Match “Normal” ZOBS Pattern 2 3 ’ 2 B ’ Polyad

3 3 ’ Follows the Rules Q(1) (III) Q(1) (II) R(1) (I) Internal Energy/cm -1 SEP Intensity “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump 4 3 ’ 3 3 ’ This points against most DD, Fermi, Coriolis interactions 2 3 ’ 2 B ’ Polyad

Interaction with 3 ’4 B ’? (No Cigar) Q(1) (III) Q(1) (II) R(1) (I) Internal Energy/cm -1 SEP Intensity “Normal” Bright State (1 2 ’ 2 3 ’) Q(1) Pump 4 3 ’ 3 ’4 6 ’ 2 3 ’ 2 B ’ Polyad

Interaction with 2 B ’ is Viable Internal Energy/cm -1 SEP Intensity 4 3 ’ 0.57[10 0, 0 0 ]+0.71[8 0, 2 0 ]+0.42[8 2, 2 -2 ] 0.92[10 2, 0 0 ]-0.14[8 0, 2 2 ]-0.30[8 4, 2 -2 ]+0.19[8 2, 2 0 ]

Conclusions Interference seen in SEP from 4 3 ’ to N B = 10 suggests that 4 3 ’ is mixed with bending polyads. Recent DVR calculations have predicted cis- mediated interactions between 4 3 ’ and 2 ’ 3 ’2 B ’. The absence of interference in 3 3 ’ probably rules out most DD/Fermi interactions.

Future Directions Calculate Franck-Condon factors for overlap of 4 3 ’ and 2 B ’ with ZOBS of N B ” = 10. Estimate mixing angles upstairs. SEP from 2 ’ 3 ’2 B ’ and from cis- 3 ’ 6 ’ to search for complimentary interferences.

Thank You FIELD GROUP Joshua Baraban Bryan Changala Monika Ciuba Tony Colombo Dr. Steve Coy Prof. Bob Field David Grimes Dr. Kirill Prozument Rachel Shaver Yan Zhou ALSO STARRING Dr. Adam Steeves Prof. Anthony Merer Prof. John Stanton (2 nd order) FUNDING!! DOE Grant DE-FG02-87ER13671

Hamiltonian for 4 3 ’ Perturbation? 4 3 ’ 2131B22131B2 cis states X0? X’?? X’’

SEP rotational selection rules  K c =0 (or 2, 4, …) K c corresponds to J in the S 0 state when ℓ=0.  K a =1 (or 3, …) K a corresponds to ℓ.  K a can be zero if axis switching is present.

SEP rotational selection rules R(1) pump J’=2, K a =1, K c =1 J’’=3, ℓ=0 (K c ’’=3) R R J’’=3, ℓ=2 (K c ’’=1) J’’=2, ℓ=2 (K c ’’=1) J’’=1, ℓ=0 (K c ’’=1) Q P R(0) pump J’=1, K a =1, K c =0 J’’=2, ℓ=0 (K c ’’=0) R J’’=2, ℓ=2 (K c ’’=0) J’’=0, ℓ=0 (K c ’’=0) R P Q(1) pump J’=1, K a =1, K c =1 J’’=2, ℓ=2 (K c ’’=1) J’’=1, ℓ=0 (K c ’’=1) R Q

SEP from 4 3 to Internal Energy/cm -1 SEP intensity J=0 ℓ=0 J=2 ℓ=2 J=2 ℓ=0 J=1 ℓ=0 J=2 ℓ=2 J=1 ℓ=0 J=2 ℓ=2 J=3 ℓ=2 J=3 ℓ=0 R(0) Q(1) R(1)

“One Bright State Per Polyad” A g 3040 cm -1 1 ’ 2 ’ 3 ’ 4 ’ 5 ’ 6 ’ A g 1386 cm -1 A g 1047 cm -1 A u 764 cm -1 B u 2857 cm -1 B u 768 cm -1 1 ” 2 ” 3 ” 4 ” 5 ”  g cm -1  g cm -1  u cm -1  u 727 cm -1  g 612 cm -1 FC active

LIF spectrum of Acetylene S B22131B2 cis interloper cis origin cis barrier transition energy/cm -1

“One Bright State Per Polyad” However, due to near-equal harmonic frequency of modes 4 ’ and 6 ’ to 5 ’’ and zero displacement, there is a Franck-Condon correlation: =  x+y,z This connects states with upstairs B excitation to downstairs zero-order states with excitation in 5 ’’. Therefore, changing v 4 ’ and v 6 ’ changes the intrapolyad intensity distribution observed in the SEP spectrum.

Structure of Acetylene S 1 —S 0 Surfaces S0S0 S1S1 Energy Bending Coordinate cm cm -1 0 cm cm cm -1 H-CCH D cm cm -1