2008 International Symposium on Molecular Spectroscopy Anion Photoelectron Spectra of CHX 2 - and CX 2 - Properties of the Corresponding Neutrals Scott Wren Kristen Vogelhuber, *Kent Ervin, **Anne McCoy, W. Carl Lineberger JILA, Department of Chemistry University of Colorado *University of Nevada, Reno **The Ohio State University June 19th, 2008

Photoelectron Spectroscopy AB - + h  AB + e - 1. Electron Affinity (EA) EA ee 2. Vibrational Frequencies,  e T0T0 3. Neutral Excited States: All above properties plus term energy, T 0 What We Measure: 4. Geometry Change, ΔR ΔRΔR

When PES is Straightforward Small geometry change between anion and neutral Resolved vibrational progressions Few isomers of anion Clear origin peak Vibrational progressions of neutral electronic states overlap minimally EA(H 2 CCN) Photoelectron Spectrum of H 2 CCN - Cyanomethyl Anion

When PES is More Challenging Large geometry change between anion & neutral Many vibrations, poorly resolved Overlapping vibrational progressions in two neutral states Origin peak very weak (due to poor Franck-Condon overlap) Anion Neutral Photoelectron Spectrum of c-C 4 F 8 - EA(c-C 4 F 8 ) TODAY we deal only with these more challenging systems

Outline How does structure of anion and neutral affect photoelectron spectrum? Halomethyl Radicals: CHX 2 Halocarbenes: CCl 2 Revisit Singlet-Triplet splitting,  E ST Contamination by CHCl 2    CHX 2 CHX 2  CCl 2  Singlet CCl 2 Nearly planar Pyramidal Triplet CCl 2

Instrumentation Photon Energy eV 364 nm Buildup Cavity Power ~100 W Resolution ~10 meV

Making Halomethyl Anions OH - + CH 2 Cl 2 CHCl H 2 O Selectively produce a single anion

CDCl 2 - Photoelectron Spectrum CDCl 2 CDCl 2 -  R C-Cl = Å  αClCCl= °  αClCH= ° Approx EA (Calculated) CDCl 2 - Cold Spectrum (~150K)

Other Halomethyl Radicals: CHBr 2 CHBr 2 CHBr 2 -  R C-Br = Å  αBrCBr= °  αBrCH= ° Approx EA (Calculated) CHBr 2 -

Other Halomethyl Radicals: CHI 2 Very similar structure and spacings to CHBr 2 and CHCl 2 Preliminary spectra— analysis and calculations are underway CHI 2 -

Other Halomethyl Radicals: CHI 2 Very similar structure and spacings to CHBr 2 and CHCl 2 Preliminary spectra— analysis and calculations are underway CHI 2 - All three halomethyl spectra exhibit complex vibrational progressions involving the H atom, with several strongly coupled modes We are currently working with Anne McCoy to model the coupled vibrations in CHX 2 All three halomethyl spectra exhibit complex vibrational progressions involving the H atom, with several strongly coupled modes We are currently working with Anne McCoy to model the coupled vibrations in CHX 2

Making Carbenes: Ion Chemistry O - + CH 2 Cl 2 CHCl OH CCl H 2 O CHCl OH Cl - + OCH 2 Cl 55% 25% 13% 6% Two main product channels!

Previous Experiments 1 1.R.L. Schwartz et al., J. Phys. Chem. A 1999, nm PES spectrum Reported both 1 A 1 and 3 B 1 states Reported Singlet- Triplet splitting  E ST = 0.13(.13) eV 1A11A1 3B13B CCl 2 - Spectrum  E ST

Previous Experiments 1 1.R.L. Schwartz et al., J. Phys. Chem. A 1999, A11A1 3B13B1 This spectrum exhibits all of the complicating features mentioned earlier, so one needs (and should have been) wary of any  E ST conclusion. All (lots!) of calculations since 1999 sharply disagree with our  E ST value  E ST Experimental resolution improved Recent experiments suggest possibility of a contaminant ion along with CCl 2 - Motivations for Reinvestigation

New “CCl 2 - ” Photoelectron Spectrum O - + D 2 CCl 2 CCl CDCl D 2 O 3B13B1 1A11A1 Differences from 1999: 351 nm Used D 2 CCl 2 Mass Bias for CCl 2 -

New “CCl 2 - ” Photoelectron Spectrum O - + D 2 CCl 2 CCl CDCl D 2 O 3B13B1 1A11A1 How might CDCl 2 - contamination affect CCl 2 - spectrum?

“CCl 2 - ” and Authentic CDCl 2 - Spectra 1A11A1 3B13B1 O - + D 2 CCl 2 CCl CDCl D 2 O Let’s subtract out the contamination

New, Clean CCl 2 - Photoelectron Spectrum 1 A 1 origin EA=1.596 eV 3 B 1 Calc 1 origin 2.5 eV Δ E ST ~0.9 eV 1 Dyke et. al.ChemPhysChem , And now Experimentalist AND Theorist are in agreement!!!

Conclusions Spectra of the halomethyl anions CHCl 2, CHBr 2, and CH I 2 reveal extensive vibrational progressions indicating a large geometry change between the ion and the neutral New photoelectron spectra of the dihalocarbenes CCl 2, CBr 2, and C I 2 show that the singlet-triplet gaps of the neutral are much larger than we had previously reported

CCl 2 - Comparison with Theory 1 1 Dyke et. al.ChemPhysChem , Exp (eV)Calc 1 (eV) 1 A 1 (0-0)1.596( )1.574(0.011) 3 B 1 (0-0)-2.475(0.021)  E ST > (0.011) 3 B 1 calculated origin  E ST much larger than previously reported Triplet origin of CCl 2 cannot be experimentally observed Singlet state of CCl 2 agrees well with theoretical predictions

Why Study Carbenes? Example: Addition of carbene into C-C double bond Same products but different mechanism based on state of carbene

Making Carbenes- Ion Chemistry Anionm/z CCl HCCl O - + H 2 CCl 2 HCCl OH CCl H 2 O  m=1 Velocity Mass Filter Resolution

Why Study Carbenes? Carbene: Contains a neutral divalent carbon atom with two nonbonding electrons Important intermediates in organic synthesis Singlet and triplet states of the neutral lie close in energy anion h 2B12B1 Singlet pp σ 3B13B1 Triplet pp σ 1A11A1 neutral