Exploring the Vibrational Structure of the Vinylidene Anion

Exploring the Vibrational Structure of the Vinylidene Anion using Argon Predissociation Spectroscopy Kristin Breen, Helen Gerardi, George Gardenier, Timothy Guasco, Jennifer Laaser, Gary Weddle, Eric Diken, and Mark Johnson Department of Chemistry, Yale University, New Haven, CT, 06511. Presented at the 64 th International Symposium on Molecular Spectroscopy June 22 -26, 2009

Outline • What is vinylidene – Facts / synthesis – Good for vibrational autodetachment • Photodetachment in vinylidene – Embedded resonances in direct detachment – Below threshold detachment • Ar-predissociation to assign vibrations • N 2 O as a messenger species

Vinylidene Important in… Acetylene pyrolysis Acetylene oxidation Interstellar medium Unsaturated carbenes in organometallic reactions

Vinylidene / Acetylene Isomerization Neutral H C=C: → H-C≡C-H H Neutral lifetime = 0. 04 -0. 2 ps Barrier height= 0. 9 – 2 kcal/mol Anion much larger barrier to isomerization Barrier height= 50 kcal/mol Ervin, K. M. ; Ho, J. ; Lineberger, W. C. J. Chem. Phys. 1989, 91, 5974 -5992.

Vinylidene Anion Synthesis Ar + N 2 O + e¯ → N 2 + O· ¯ + H 2 C=CH 2 OH· + H 2 C=CH¯ OH¯ + H 2 C=CH· → H 2 O + H 2 C=C¯ 2 k. J/mol* Relative Intensity 100 k. J/mol* 10 Ar + N 2 O + C 2 H 4 15 20 25 Ion Mass (m/z) *Lee, J. ; Grabowski, J. J. Chem. Rev. 1992, 1611 -1647. 30 35

Experimental Set-up pulsed valve bi-plane reflectron photoelectrons ion beam drift tube MCP neutral detector 1 ke. V electron gun MCP ion detector YAG 1064 nm OPO/OPA mid - IR (600 -4500 cm-1)

Photodetachment data Below threshold detachment Embedded resonances in direct detachment VDE ~3950 cm-1 2500 3000 3500 Photon Energy (cm-1) 4000 4500

Ar Predissociation Spectroscopy Aˉ·Arm + hn → Aˉ·Arn + (m-n)Ar

Anion Vibrations Argon Loss Signal H 2 CC– D 2 CC– 1600 1800 2000 2200 2400 2600 2800 3000 3200 Photon Energy (cm-1) 3400 3600 3800 4000 4200 4400

Anion Vibrations CH(D) symmetric 2606 (1954) cm-1 H 2 CC– CH(D) asymmetric 2664 (1979) cm-1 Argon Loss Signal overtone of CH 2 scissors 2749 cm-1 Fermi resonances important with CH symmetric and 2 quanta of CH 2 scissors D 2 CC– E 1600 1800 2000 2200 2400 Photon Energy (cm-1) 2600 2800

Anion Vibrations CC stretch with CH(D) asym. and sym. stretches H 2 CC¯ 1 st overtone of CC stretch CH stretch with CH 2 scissors overtone of CC or CD stretch with CD 2 scissors D 2 CC¯ 1 st overtone of sym & asym stretches 2800 3000 3200 3400 3600 3800 Photon Energy (cm-1) 4000 4200 4400

Different Messenger Species… H 2 C=C¯·X X = N 2 O ~ 41 cm-1 splitting X = Ar ~ 52 cm-1 splitting 3800 3900 4000 4100 4200 4300 4400 Photon Energy (cm-1)

Photodetachment Data Below threshold CH stretches detachment Embedded resonances Combination bands of in. CH direct detachment & CC stretches VDE ~3950 cm-1 2500 3000 3500 Photon Energy (cm-1) 4000 4500

Conclusions • assigned peaks to photodetachment spectrum of vinylidene by using Ar-predissociation / isotopic substitution – above threshold resonances • combination bands • overtones – below threshold detachment • fundamentals • fermi resonances • shown messenger species effect

Acknowledgements Mark Johnson Helen Gerardi George Gardenier Timothy Guasco Gary Weddle Rachael Relph Ben Elliott Mike Kamrath Christopher Leavitt