RI14, 61st OSU Symposium

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61st OSU International Symposium on Molecular
Spectroscopy RI14
Assignment of GG, GG, TT, and TG conformers in
the FASSST rotational spectrum of
n-propanol Zbigniew Kisiel, Orest
Dorosh Institute of Physics, Polish Academy of
Sciences Atsuko Maeda, Frank C. De Lucia, Eric
Herbst Department of Physics, The Ohio State
University
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TT
TG (two identical)
Rotation of CH2OH about CC
Rotation of OH about CO
GG
GT
GG
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Most relevant previous studies

• Abdurakhmanov et al. several papers over the
  period 1967-1987, cm-wave rotational studies of
  n-propanol.
• gauche form estimated to be the most stable one.
• Dreizler Scappini, Z.Naturforsch. 36a, 1187
  (1981) b-type cm-wave rotational spectrum
  of the TT species
• Maeda et al. , Astrophys. J. Suppl. Ser. 162, 428
  (2006) over 2400 lines of the GT conformer up to
  375 GHz assigned and fitted
• Kahn Bruice, Chem.Phys.Chem. 6, 487 (2005)
  detailed ab initio analysis of relative energies.
  In the preferred result GT is the global minimum
  with GG, GG at 38, 52 cm-1 resp., TT,TG are at
  28,45 cm-1 resp.

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Ab initio spectroscopic observables for
n-propanol
GT GG GG TT
TG A /MHz 14339 14100 14216
26579 26147 B 5102 5019
5034 3784 3734 C 4307
4280 4227 3531 3508 DJ /kHz
5.40 5.09 5.54 0.828 0.840
DJK -23.8 -21.7 -25.9 -2.35
-2.61 DK 64.1 58.4 69.6
58.7 57.6 dJ 1.59 1.43
1.65 0.0737 0.0737 dK 11.9
10.1 11.2 0.361 1.10
m_a /D 0.71 0.56
1.39 0.09 1.15 m_b 0.87
1.04 0.12 1.46 0.39 m_c
0.96 1.09 0.87 0 1.15
m_tot 1.48 1.61 1.65
1.46 1.68
Unscaled B3LYP/6-31G(d,p)
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Confirmation of the assignment of the GT conformer
GT gs ? 1 ab
initio A /MHz 14330.37308(45)
14378.5960(21) 14339 B
5119.30843(16) 5104.59867(93) 5102 C
4324.20213(16) 4318.31841(57) 4307
DJ /kHz 5.66401(22) 5.74650(85)
5.40 DJK -24.6960(11) -26.4520(35)
-23.8 DK 67.8861(38)
75.088(12) 64.1 dJ
1.687806(53) 1.71737(36) 1.59 dK
12.56606(88) 13.027(14) 11.9
N
2861 308 s /kHz 63.1
83.1
Unscaled B3LYP/6-31G(d,p)
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Cavity-FTMW Stark measurements for GT n-propanol
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Dipole moments for GT and TT n-propanol
DFT and MP2 with 6-31G(d,p) give
ma?0.1 D
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Bands in the FASSST spectrum
MHz
Typical band spacing B C for R-type bands 2A
(B C) for Q-type bands
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Band A J 17 ?16 of GG
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Band C Ka 9 ? 8 cQbQ of GG (white left),
GG (white right), GT (yellow right)
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Distribution of mixing coefficients and data
points
1 Pmix
GG
GG
GG
GG
obs-calc
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Comparison of spectroscopic constants

• GT GG
  GG
• A /MHz 14330.37308(45) 14206.741(25)
  14258.160(25)
• B 5119.30843(16) 5036.7229(41)
  5050.7618(39)
• C 4324.20213(16) 4290.3029(27)
  4253.6136(25)
• DJ /kHz 5.66401(22) 5.36149(75)
  5.22356(91)
• DJK -24.6960(11) -23.261(12)
  -24.019(28)
• DK 67.8861(38) 63.384(57)
  68.923(62)
• dJ 1.687806(53) 1.51462(33)
  1.54892(39)
• dK 12.56606(88) 11.244(20)
  11.604(18)
• DE/MHz
  90988.67(11)
• N 2861 3114
• s /kHz 63.1 103.9
• ab initio B3LYP/6-31G(d,p)

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Effective fit for TT

• TT ab
  initio
• A /MHz 26401.5164(50) 26579
• B 3802.15219(57) 3784
• C 3549.46158(60) 3531
• DJ /kHz 0.99790(43) 0.828
• DJK 0.302(62) -2.35
• DK 153.9(17) 58.7
• dJ 0.12508(46) 0.0737
• dK -9.20(18) 0.361
• N 232
• s /MHz 0.11 but only to Ka0..2

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The torsional potential section giving rise to
TT, TG, TG- states is analogous to that for
ethanol that results in T, G, G- states. But
for ethanol E(G) - E(T) ? 40 cm-1 and a single
state fit is possible for a broad range of
T-state transitions.
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Band B J 31 ?30 of TG
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Ka 9, aR-type transitions for TG
Analogous aR-type bands for TG-
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Preliminary coupled fit for TT?TG

• TT TG
  
• A /MHz 26422.79(91) 25524.7(82)
• B 3802.3984(63) 3769.085(49)
• C 3549.4244(18) 3535.270(19)
• DJ /kHz 1.0052(14) 0.9050(50)
• DJK -2.4 -2.606
• DK 58.7 57.6
• dJ 0.12428(77) 0.0974(54)
• dK 0.36 1.096
• DE/MHz 352043.(884)
• N 740
  
• ab initio B3LYP/6-31G(d,p)
• A /MHz 26579 26147

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Principal conclusions

• TT, TG, GT, GG, GG conformers have been assigned
  with confidence in the FASSST spectrum and all
  major bands are accounted for
• GGGG conformers are satisfactorily fitted in a
  coupled fit resulting in DE(GG- GG) 3.035
  055(4) cm-1
• TT conformer is perturbed beyond Ka1, TG
  conformer is perturbed even from Ka0, for both
  TG and TG- substates.
• TT , TG and TG are more mutually perturbed and
  are thus closer to each other than T, G and G
  in ethanol
• Three state fits are still required
• GT?GG?GG would yield DE(GG- GT)
• TT ?TG ? TG- is needed even for satisfactory
  description of the spectrum, and of course for
  DEs

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