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UV Spectroscopy of 3-phenyl-2-propynenitrile
KHADIJA JAWAD, AND TIMOTHY S. ZWIER 71st International Symposium on Molecular Spectroscopy TG07 Department of Chemistry, Purdue University West Lafayette, IN 47906
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Motivation Previous work on photochemical reaction between diacetylene and benzene yielded phenyldiacetylene 3-phenyl-2-propynenitrile (PPN) structurally similar to phenyldiacetylene Photochemical reaction between benzene and cyanoacetylene could produce PPN Spectroscopic signature of PPN important to confirm its production 2053 cm-1 Robinson, A.G., P.R. Winter, C. Ramos, and T.S. Zwier, J. Phys. Chem. A, 2000, 104,
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Experimental: Resonant Two-photon Ionization (R2PI)
Supersonic Expansion Sample heated to 60°C Ion Chamber Laser Ports 2 Stage Ion Acceleration Einzel Lens Pulsed Valve MCP Time-of-Flight Tube Mass Gate Pulser Vibrationally cooled to zero-point levels S0
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Experimental: Laser-Induced Fluorescence
Laser Induced Fluorescence Chamber
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2C-R2PI Overview Spectrum
2750 nm nm TSZ: I added the wavelengths in nm since others may be more familiar with this unit. Is this a 1C-R2PI spectrum? 292 nm 208 nm
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2C-R2PI Overview Spectrum
Tentative origin at 35,242 cm-1 I would avoid giving them the impression that the 472/452/491 is a FC progression, since in later slides when we look more carefully, this is not necessarily what we think.
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Excited State Lifetime
Bi-exponential decay pattern: Short-lived component ≤ 10 ns Long-lived component > 800 ns M+ + e ISC Excited state calculations using TD-DFT were performed with a ωB97X-D basis set at 6-31+G(d) level of theory.
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LIF Spectrum Remove one of the scans in the overlap region – we can see that there are two lines around and possibly around (?). Use the scan with the more intense transitions in the overlap region.
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Dispersed Fluorescence from 35242 cm-1 band
Scattered light TSZ: Put in a slight offset to raise the baseline off the bottom axis of the graph. Move the 0 to near the right-hand edge, and add in another 200 cm-1 of the DFL spectrum.
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Comparison to Calculation
Experimental wB97X-D 6-31+G(d) B3LYP G(d,p) ν (cm-1) Symmetry 73 B2 71 78 B1 77 74 207 209 198 233 237 232 371 A1 370 391 394 385 412 A2 409 405 479 514 509 516 532 541 598 601 591.98 624 615 630 591.91 643 637 638 686 706.63 698 699 707.45 701 702 783 772 774 874 856 855 937 960 940 941 985 984 978 976 1008 987 1007 1027 1010 1005 Only two a1 fundamentals in first 800 cm-1
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How are b1 fundamentals gaining intensity in emission?
C2ν Cs A2 A1 b1 a1 b2 S1 S2 Vibronic coupling S0 Optimized S1 geometry: In-plane deformation of C3N chain A1xb1=B1 S6 B2 A’ S5 A1 A’ S4 B2 A’ S3 A2 A” S2 A1 A’ A2xb2=B1 S1 A2 A” b2 member of tunneling doublet can mix with b1 fundamentals in S2(A1) state Forbidden in C2v Oscillator strength S0-S S0-S S0 A1 A’
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Vibrations of C3N group appear in pairs:
b1 and b2 Experimental wB97X-D 6-31+G(d) B3LYP G(d,p) ν (cm-1) Symmetry 73 B2 71 78 B1 77 74 207 209 198 233 237 232 371 A1 370 391 394 385 412 A2 409 405 479 514 509 516 532 541 598 601 591.98 624 615 630 591.91 6b 643 637 638 686 706.63 698 699 707.45 701 702 783 772 774 874 856 855 937 960 940 941 985 984 978 976 1008 987 1007 1027 1010 1005
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Vibrations involved in b1-b2 pairs
b2 71cm-1 b1 74cm-1 b2 232cm-1 b1 198cm-1 b2 516cm-1 b1 532cm-1
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Molecular Orbitals Visualized
(LUMO) (LUMO) (HOMO) S0-S1 S0-S2
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Summary R2PI spectrum recorded from 34,000-48,000 cm-1
Possible S0-S1 origin at 35,242 cm-1 Sharp peaks up to 37,000 cm-1 Broad absorptions similar to phenyldiacetylene above 37,000 cm-1 Presence of short-lived (≤10ns) singlet and long-lived excited state (>800ns) Peak at lower wavenumber than origin in LIF Dispersed fluorescence of origin lacks a1 vibrational fundamentals Points to importance of vibronic coupling Consistent with S0-S1 dipole forbidden in C2v Prominent peaks can be assigned to b1 fundamentals b1 vibrations appear alongside corresponding b2 Possible coupling to S2 state
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Future Work Dispersed fluorescence on more peaks in the excitation spectrum Determine identity of 35,242cm-1 peak: High Res UV (?) Photochemically react cyanoacetylene and benzene
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Acknowledgments Professor Timothy Zwier Zwier Group
Dr. Deepali Mehta-Hurt Dr. Joseph Korn Professor Lyudmila Slipchenko Carlos Borca
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How are b1 fundamentals gaining intensity in emission?
C2ν Cs A2 A1 b1 a1 b2 S1 S2 Vibronic coupling S0 Optimized S1 geometry: In-plane deformation of C3N chain A1xb1=B1 S6 B2 A’ S5 A1 A’ S4 B2 A’ S3 A2 A” S2 A1 A’ A2xb2=B1 S1 A2 A” b2 member of tunneling doublet can mix with b1 fundamentals in S2(A1) state Forbidden in C2v Oscillator strength S0-S S0-S S0 A1 A’
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Calculated Geometry changes
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Pertinent Character Tables
Cs
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