1. and analysis of hyperfine structure from four quadrupolar nuclei
71st International Symposium on Molecular Spectroscopy WE06
Rotational spectroscopy of CF2ClCCl3
and analysis of hyperfine structure
from four quadrupolar nuclei
Zbigniew Kisiel, Ewa Białkowska-Jaworska, Lech Pszczółkowski,
Institute of Physics, Polish Academy of Sciences, Warszawa, Poland
Iciar Uriarte, Francisco J. Basterretxea, Emilio J. Cocinero
Departamento de Quimica Fisica, Universidad del Pais Vasco,
(UPV-EHU), Bilbao, Spain

2. Johannes C. Laube et al.,
Praha2008
Analysis of air samples from Tasmania +
Analysis of air bubbles in Greenland snow
Four previously undetected ozone-depleting substances identified:
CFC-112 = CFCl2CFCl2
CFC-112a = CF2ClCCl3
CFC-113a = CF3CCl3
HCFC-133a = CF3CH2Cl
CFC-112a = CF2ClCCl3 has not yet been studied by rotational spectroscopy (small  , b-type spectrum and 4Cl)

3. The chirped-pulse rotational spectrum of CF2ClCCl3:
Praha2008
CFC-112a 
parent
551  440
550  441
transition region
Cl2
Cl1
Cl3
Initial A,B,C determined

4. Hyperfine structure (4 chlorine nuclei):
Praha2008
CFC-112a
441  330
440  331
Obs.
3 asymmetric rotor quantum numbers + 4 spin quantum numbers = 7:
Fortunately symmetric top quantisation allows using = 6 quanta
First
prediction

5. Praha2008
Predictions:
Accurate predictions of hyperfine structure are the key to success. There are several possibilities:
Use the W.C.Bailey approach: ab initio calculation at equilibrium geometry with extended basis set tailored to the specific quadrupolar nucleus, see:
Use general scaling coefficients: see
Białkowska-Jaworska et al., J.Mol. Spectrosc.
238, 72 (2006)
Use specific scaling based on related molecules:
H-CCl3, H3C-CCl3, NC-CCl3
SPFIT/SPCAT package is the tool of choice, but the standard (32-bit) compilation runs into „Memory allocation error” for this molecule (Hamiltonian sizes > 7800).
64-bit executables for Windows and Linux are now available on the PROSPE website:

6. Chirped pulse identification allowed making F-P scans:
Praha2008
Chirped pulse identification allowed making F-P scans:
431  322
Chirped pulse
FWHH  90 kHz
FWHH  18 kHz
Cavity

7. F-P scans allowed assignment:
Praha2008
Pattern matching becomes possible
441  330
440  331
Obs.
transition in the fit
Calc.

8. And in more detail: 441  330 440  331 Obs. Calc.
Praha2008
And in more detail:
441  330
440  331
Obs.
Complex blends are avoided and only clear transitions picked out for analysis
Calc.

9. Also for the 431  322 transition:
Praha2008
Also for the 431  322 transition:
Obs.
Calc.

10. And in more detail: Obs. 431  322 Calc. Settable frequency marker
Praha2008
And in more detail:
Obs.
431  322
Settable frequency marker
(V and ^V in ASCP_L)
Calc.

11. Rotational and centrifugal constants:
Praha2008
Rotational and centrifugal constants:
chirped/ASFIT cavity/SPFIT MP2/aug-cc-pVTZ
A /MHz (32) (84)
B /MHz (63) (10)
C /MHz (31) (10)
DJ /kHz [ ] (27)
DJK /kHz [ ] [ ]
DK /kHz [ ] [ ]
dJ /kHz [ ] [ ]
dK /kHz [ ] [ ]
Nlines
Ntrans
sigma /kHz
rms
The number of different measured frequencies
The number of different rotational transitions

12. Nuclear quadrupole coupling constants:
Praha2008
predicted experimental
scaled Bailey SPFIT
Cl1 = in-plane Cl in the CCl3 group:
1.5Xaa /MHz (66)
(Xbb-Xcc)/4 /MHz (22)
Xab /MHz (12)
Cl2 = out-of-plane Cl in the CCl3 group:
1.5Xaa /MHz (37)
(Xbb-Xcc)/4 /MHz (84)
Xab /MHz (80)
Xac /MHz (19)
Xbc /MHz (43)
Cl3 = in-plane Cl in the CF2Cl group:
1.5Xaa /MHz (64)
(Xbb-Xcc)/4 /MHz (24)
Xab /MHz (12)
Average prediction accuracy:
scaled 2.2 %
Bailey 3.1 %

13.  Principal nuclear quadrupole tensors: aa ab ac za zz 0 0
Praha2008
Principal nuclear quadrupole tensors:
aa ab ac
ab bb bc
ac bc cc
zz
0 xx 0
yy 
 = (xx - yy)/zz
za
QDIAG
zz = (12) MHz
 = (15)
zz = (3) MHz
 = (21)
zz = (12) MHz
 = (15)
H-CCl zz = (18) MHz F-CC-Cl zz = (1) MHz
H3C-CCl3 zz = (14) MHz

14. Praha2008
CONCLUSIONS:
Assigning completely resolved quadruple quadrupolar problems is possible but accurate prediction is the key to success
Suitable combination of supersonic expansion techniques was important for CFC-112a : initial assignment with chirped pulse and follow up measurements with the cavity
The hyperfine information for CF2ClCCl3 allows interesting comparisons with other molecules such as related triple-chlorine molecules CHCl3, CH3CCl3 and with chloro-fluoro species
The hyperfine angles za provide useful additional information for structure determination
The CFC-112a molecule has been „tamed”: basic high resolution spectroscopic constants have been determined