1. 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

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

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

4. Chemical Physics Letters 447 (2007) 202–207
I’ : cm-1 (v12+v14)
II’ : 1226 cm-1 (v10+v15)
III’ : 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.

5. FTIR spectrum of HCOOH at room temperature

6. 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)

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

8. a-type Q-branch
Observed
Simulated
* Monomer lines

9. 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

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

11. 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, (2014)

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

13. 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, (2006)

14. 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 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.