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
TT
TG (two identical)
Rotation
of CH2OH
about CC
GT
Rotation of OH about CO
GG
GG’
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.
Ab initio* spectroscopic observables for n-propanol:
A
B
C
/MHz
DJ /kHz
DJK
DK
dJ
dK
GT
GG
14339
5102
4307
14100
5019
4280
GG’
14216
5034
4227
TT
26579
3784
3531
TG
26147
3734
3508
5.40
-23.8
64.1
1.59
11.9
5.09
-21.7
58.4
1.43
10.1
5.54
-25.9
69.6
1.65
11.2
m_a /D
m_b
m_c
0.71
0.87
0.96
0.56
1.04
1.09
1.39
0.12
0.87
0.09
1.46
0
1.15
0.39
1.15
m_tot
1.48
1.61
1.65
1.46
1.68
* Unscaled B3LYP/6-31G(d,p)
0.828
-2.35
58.7
0.0737
0.361
0.840
-2.61
57.6
0.0737
1.10
Satellite line
sequence (GT
excited state)
Ka = 1- 0 of GT
Confirmation of the assignment of the GT conformer
GT gs
A
B
C
/MHz
DJ /kHz
DJK
DK
dJ
dK
N
s
/kHz
14330.37308(45)
5119.30843(16)
4324.20213(16)
5.66401(22)
-24.6960(11)
67.8861(38)
1.687806(53)
12.56606(88)
2861
63.1
* Unscaled B3LYP/6-31G(d,p)
 =1
14378.5960(21)
5104.59867(93)
4318.31841(57)
5.74650(85)
-26.4520(35)
75.088(12)
1.71737(36)
13.027(14)
308
83.1
ab initio*
14339
5102
4307
5.40
-23.8
64.1
1.59
11.9
Cavity-FTMW Stark measurements for GT n-propanol
Dipole moments for GT and TT n-propanol
DFT and MP2 with
6-31G(d,p) give
ma0.1 D
Bands in the FASSST spectrum:
Band system A @ 9.35 GHz
Band system B @ 7.2 GHz
Band system C @ 19.15 GHz
MHz
Typical band spacing: B + C for R-type bands
2A – (B + C) for Q-type bands
Band A:
J = 17 16 of GG’
Band C:
Ka = 9  8 cQ+bQ of GG (white left),
GG’ (white right),
GT (yellow right)
Distribution of mixing coefficients and data points:
1 – Pmix
obs-calc
GG
GG’
GG
GG’
Comparison of spectroscopic constants:
GT
A
B
C
/MHz
DJ /kHz
DJK
DK
dJ
dK
14330.37308(45)
5119.30843(16)
4324.20213(16)
5.66401(22)
-24.6960(11)
67.8861(38)
1.687806(53)
12.56606(88)
DE/MHz
N
s
/kHz
ab initio
A
B
C
/MHz
GG
GG’
14206.741(25) 14258.160(25)
5036.7229(41) 5050.7618(39)
4290.3029(27) 4253.6136(25)
5.36149(75)
-23.261(12)
63.384(57)
1.51462(33)
11.244(20)
5.22356(91)
-24.019(28)
68.923(62)
1.54892(39)
11.604(18)
90988.67(11)
2861
3114
-1
E(GG’)
E(GG)
=
3.035
055(4)
cm
63.1
103.9
B3LYP/6-31G(d,p)
ab initio  14 cm-1
14339
14100
14216 *
-1
5102 E(GG) - E(GT)
5019 *40 cm ? 5034
4307
4280 (three
*
4227
state fit required)
Effective fit for TT:
TT
A
B
C
ab initio
/MHz
26401.5164(50)
3802.15219(57)
3549.46158(60)
DJ /kHz
DJK
DK
dJ
dK
0.99790(43)
0.302(62)
153.9(17)
0.12508(46)
-9.20(18)
N
s
232
0.11 but only to Ka=0..2
/MHz
26579
3784
3531
0.828
-2.35
58.7
0.0737
0.361
!
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.
Band B:
J = 31 30 of TG+
Ka = 9, aR-type
transitions for TG+
Analogous aR-type
bands for TG-
Ka = 0, aR-type
transitions for TG+
Ka = 0, aR-type
transitions for TG-
Preliminary coupled fit for TTTG+ :
TG+
TT
A
B
C
/MHz
DJ /kHz
DJK
DK
dJ
dK
26422.79(91)
3802.3984(63)
3549.4244(18)
1.0052(14)
[-2.4]
[58.7]
0.12428(77)
[ 0.36]
DE/MHz
0.9050(50)
[-2.606]
[57.6]
0.0974(54)
[ 1.096]
352043.(884)
N
740
ab initio
A
B
C
25524.7(82)
3769.085(49)
3535.270(19)
/MHz
E(TG+) - E(TT)= 11.44(3) cm-1
ab initio  17 cm-1
B3LYP/6-31G(d,p)
26579
3784 *
3531
26147 *
3734
3508
Principal conclusions:
TT, TG, GT, GG, GG’ conformers have been assigned with
confidence in the FASSST spectrum and all major bands are
accounted for
GG+GG’ conformers are satisfactorily fitted in a coupled fit
resulting in DE(GG’- GG) = 3.035 055(4) cm-1
TT conformer is perturbed beyond Ka=1, TG conformer is
perturbed even from Ka=0, 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 DE’s