1. Ivan Antonov, Beau Barker, Vladimir Bondybey and Michael Heaven Emory University Department of Chemistry Atlanta, GA

2. D e (cm -1 ) R e (Å) w e (cm -1 ) Ar 2 923.8326 Mg 2 4303.9751 Be 2 929.72.45275.8 Li 2 84402.67351 1S 1u1u 1g1g 2S 2u2u 2g2g Early controversy over an inner “deep” minimum or an outer shallow minimum. Why? Be dimer is a very complicated system...

3. Why + ? 1S 1u1u 1g1g 2S 2u2u 2g2g D e + (cm -1 ) R e (Å) Δ G 1/2 (cm -1 ) Be 2 + exp 16321(40) 498(20) Be 2 + theor 166842.211516 Be 2 Be+Be Be 2 + +e - Be+Be + +e - DeDe De+De+ IP(Be 2 ) IP(Be)

4. Mass-selected REMPI spectrometer

5. PFI-ZEKE time sequence and excitation scheme Extractor Repeller -5.1 V -7.1 V 1 st laser 2 nd laser Gas pulse 1.7 μs Ablation laser

6. Broad PFI-ZEKE scan of Be 2 + First laser at B-X 2-0 transition

7. Rotational structure of Be 2 + at v + =1 line a)Excitation through B-X 2-0 R(1) line b)Excitation through B-X 2-0 R(2) line Ground state of Be 2 + is X 2 Σ u + by nuclear spin symmetry; B 0 =0.760 cm -1 ; r 0 =2.212 Å

8. ΔE=1.6464*F 1/2 IP=59824(2) cm -1 IP from PIE was estimated as 59828(40) cm -1 PFI-ZEKE Determination of IP of Be 2

9. Vibrational levels of Be 2 + RKR inversion turning points of Be 2 + and a Morse curve fit B e =0.765 cm -1 α e =0.0103 cm -1 r e =2.211 Å

10. Measured and calculated constants of Be 2 +

11. D e (cm -1 ) LiBe2420 Li 2 - 7315 Be 2 + 16438 Molecules Isoelectronic to Be 2 + 1S 1u1u 1g1g 2S 2u2u 2g2g

12. Conclusions Be 2 + has (X 2 Σ u + ) ground state IP value of Be 2 is measured at 59 824(2) cm -1 D e + is 16 438 (5) cm -1 Morse potential energy curve is close in form to the vibrational levels of Be 2 + Recent high-level and DFT theoretical calculations are in respectable agreement with Be 2 + parameters Be 2 + has uniquely high bond strength among the isoelectronic diatomic molecules Li 2 - and LiBe Acknowledgements: NSF for funding