Chuanxi Duan (段传喜） Central China Normal University Wuhan, China 69th Meeting - June 16-20, 2014 Champaign-Urbana, Illinois High resolution jet-cooled infrared absorption spectra of the formic acid dimer: a reinvestigation of the C-O stretch region Chuanxi Duan (段传喜） Central China Normal University Wuhan, China

Double proton transfer in formic acid dimer (HCOOH)2 Tunneling splitting of proton transfer: Rotational spectroscopy X High-resolution infrared laser spectroscopy √

observed E- E+ E+ < E- simulated E+ > E- E+: tunneling level with spatially symmetric wavefunction. E-: tunneling level with spatially anti-symmetric wavefunction.

Chemical Physics Letters 447 (2007) 202–207 I’ : 1220.5 cm-1 (v12+v14) II’ : 1226 cm-1 (v10+v15) III’ : 1234.7 cm-1 (v22) No strong monomer band was assumed to be present in this region. Vibrational numbering with the notation of Bertie et al., J. Chem. Phys. 76 (1982) 886.

FTIR spectrum of HCOOH at room temperature

Absorption spectrum in the slit jet expansion of HCOOH diluted in Ne Experimental conditions: diode laser rapid scan slit nozzle multi-pass cell (ν5 fundamental band)

Jet-cooled absorption spectrum of HCOOH monomer (v5 fundamental band) (T=12 K)

a-type Q-branch Observed Simulated * Monomer lines

D2h C2h C2h B3u B2u Bu Au ν =1 ν =1 B1u Au B3g Ag ν =0 Ag vibration a-type b-type c-type vibration Vibration-tunneling vibration

Experimental: I’ : 1219.7 cm-1 II’ : 1225.3 cm-1 III’ : 1233.9 cm-1 F. Kollipost, et al, J. Chem. Phys. 136, 151101 (2012). Experimental: I’ : 1219.7 cm-1 II’ : 1225.3 cm-1 III’ : 1233.9 cm-1 1228 1166 II : v10+ v15 √ I : v12+v14 ??? III : v22 √ I : v23+2 v24 √ 1226 1226 x2 x2

Molecular constants of (HCOOH)2 (in cm-1) b b M. Ortlieb and M. Havenith, J. Phys. Chem. A 111, 7355 (2007). ΔE = Eu – El El = E+ , Eu = E- Kusse G. Goroya et al, J. Chem. Phys. 140, 164311 (2014)

Molecular constants of (HCOOH)2 (in cm-1) ΔE = Eu – El El = E+ , Eu = E- Kusse G. Goroya et al, J. Chem. Phys. 140, 164311 (2014)

Deperturbation analysis of the Fermi-triad system H is underdetermined unless with some conditions: assuming only one bright state, two dark states relative band (line) intensities additional constraint on the coupling constants …… I. M. Konen et al., J. Chem. Phys. 125, 074310 (2006)

Conclusions Vibration-rotation-tunneling spectra are measured and analyzed for the Fermi-triad system of (HCOOH)2 in the C-O stretch region. A different assignment for the combination band centered at 1219.7 cm-1 is proposed. The energy order of the tunneling levels in the vibrationally excited states is found to be reserve due to Fermi resonance. A reliable deperturbation analysis is still not available.