THE MICROWAVE SPECTRA OF THE LINEAR OC HCCCN,
OC DCCCN, AND THE T-SHAPED HCCCN CO2 COMPLEXES
The 62nd. International Symposium on Molecular Spectroscopy, RG 09
LU KANG
Department of Natural Sciences, Union College, Barbourville, KY 40906
STEWART E. NOVICK
Department of Chemistry, Wesleyan University, Middletown, CT 06459
General Introduction

IR study of the OC---HCCCN, and the HCCCN---CO2
X. Yang, R.Z. Pearson, G. Scoles; Chem. Phys. Lett., 204(12), p145, 1993
X. Yang, R.Z. Pearson, and G. Scoles; J. Mol. Spectrosc., 180(1), p1, 1996

Rotational spectroscopy study of the OC---HCN
E. J. Goodwin, A. C. Legon; Chem. Phys., 87, p81, 1984

Both Linear and T-shaped HCN---CO2 exist
T. D. Klots, R. S. Ruoff, H. S. Gutowsky; J. Chem. Phys., 90(8), p4216, 1989
K. R. Leopold, G. T. Fraser, W. Klemperer; J. Chem. Phys., 80(3), p1039, 1984

Complete rotational spectroscopy investigations of the weakly
bound Ng---HCCCN van der Waals complexes
He---HCCCN: W. C. Topic, W. Yäger; J. Chem. Phys.,123(6), p064303/1, 2005
Ne---HCCCN: A. Huckauf, W. Yäger; manuscript in preparation.
Ar---HCCCN: A. Huckauf, W. Yäger, P. Botschwina, R. Oswald; J. Chem. Phys.,
119(15), p7749, 2003

Thorough understanding of the subunits: CO and HCCCN
CO: F. J. Lovas, P. H. Krupenie; J. Phys. Chem. Ref. Data, 3(1), p245, 1974
HCCCN: W. J. Lafferty, F. J. Lovas; J. Phys. Chem. Ref. Data, 7(2), p441, 1978
Experiment

Balle-Flygare Type Fourier transform microwave spectrometer
(FTMW) at Wesleyan University




The synthesis of Ethyl cyanide (Cyanoacetylene), HCCCN.


H



Molecular beam pulsed-nozzle (~3 K)
Cover 3.7 – 26.5 GHz
~ 1 kHz frequency resolution
C. Moureu, J. C. Bongrand; Ann. Chim. (Paris), 14, p47, 1920.
Propiolamide is commercially available (Acme Bioscience Inc.)
O
120 - 140 oC
+ P2O5
C
C
C
H C
C
C
N
sand
NH2
Deuterated sample, DCCCN was also made!
0.5% HCCCN (DCCCN) + 7.5% CO / Ar or Ne carrier gas
0.5% HCCCN (DCCCN) + 10% CO2 / Ar or Ne carrier gas
Spectrum
Spectrum
Hamiltonian




H = HR + HQ
HR: the effective Hamiltonian for the vibrational ground
state semi-rigid linear molecules
HR = B0J2 – D0J4 + H0J6
EJ = B0J(J+1) – D0J2(J+1)2 + H0J3(J+1)3

3 + H (J+1)3[(J+2)3-J3]
=
2B
(J+1)
–
4D
(J+1)
J+1→J
0
0
0
HQ: the nuclear quadrupole coupling interactions
between the molecular rotation angular momentum, J,
and the nuclear spin angular momentum, I.
1
HQ =  Q : E
6
The nuclear spin of Nitrogen atom is1, hence, J + I(N) = F
Spectroscopic constants
Table-1: the rotational constants, centrifugal distortion constants, and the nuclear
quadrupole coupling constants of the OC---HCCCN isotopomers
Molecular Species
(Hydrogenated)
σ (kHz) /
D0
(kHz)
OC --- HCCCN
591.143890(36)
0.29866(29)
-0.386(67)
-4.2097(19)
1.4 / 32
O13C --- HCCCN
611.097110(30)
0.31732(21)
-1.52(49)
-4.2085(10)
1.0 / 44
OC --- HCCCN
619.521775(21)
0.32577(11)
-0.39(18)
-4.20865(55)
0.74 / 72
OC --- H13CCCN
619.376060(39)
0.32520(28)
-0.47(55)
-4.2123(19)
1.0 / 32
OC --- HC13CCN
617.799558(32)
0.32443(23)
-1.10(47)
-4.2085(15)
1.0 / 37
OC --- HCC13CN
613.348720(32)
0.31871(23)
-0.05(47)
-4.2096(20)
0.72 / 38
OC --- HCCC15N
607.553100(56)
0.30901(23)
-0.70(68)
N/A
0.85 / 14
18
H0
(Hz)
eqQ(14N)
(MHz)
B0
(MHz)
#
o
f
l
i
n
e
s
Spectroscopic constants
Table-1: the rotational constants, centrifugal distortion constants, and the nuclear
quadrupole coupling constants of the OC---DCCCN isotopomers
Molecular Species
(Deuterated)
18
B0
(MHz)
D0
(kHz)
eqQ(14N)
(MHz)
H0
(Hz)
# of lines /
σ (kHz)
OC --- DCCCN
591.397792(45)
0.28887(37)
2.76(92)
-4.354(65)
3.0 / 28
O13C --- DCCCN
611.289802(30)
0.30730(29)
-0.02(65)
-3.928(35)
1.9 / 36
OC --- DCCCN
619.654917(32)
0.31430(25)
-0.58(58)
-4.21113(66)
1.8 / 57
OC --- D13CCCN
N/A
N/A
N/A
N/A
N/A
OC --- DC13CCN
617.915477(39)
0.31292(29)
-1.85(66)
-4.244(35)
1.7 / 33
OC --- DCC13CN
613.442390(39)
0.30814(30)
1.45(67)
-4.125(35)
2.3 / 35
OC --- DCCC15N
607.631979(78)
0.30238(72)
0.0102(20)
N/A
3.5 / 11
Spectroscopic constants of HCCCN---CO2
Table-3: The spectroscopic constants
of the T-shaped HCCCN---CO2 dimer
*
Constants
A / MHz
11824
B / MHz
764.597(3)
C / MHz
715.745(2)
ΔJ / kHz
0.5006(7)
ΔJK / kHz
120.89(4)
δJ / kHz
0.0425(11)
δK / kHz
0.0653(6)
HJ / kHz
1.2(11) 10-6
HJK / kHz
0.03488(9)
HKJ / kHz
-0.683(3)
HK / kHz
2.52779(5)
χaa / MHz
-4.1293(3)
χbb – χcc / MHz
0.10(8)
σ / kHz
1
#
o
f
l
i
n
e
s
2
.
1
5
4
*: The standard deviations are put in the ( ).
: Fixed to HCN---CO2 value, 0.394406 cm-1.
 The observed spectra agree with
the T-shaped structure.
 IR spectroscopy determined
rotational constants:
B” = 0.0254463(59) cm-1
i.e., 762.9(19) MHz
C” = 0.0254463(59) cm-1
i.e., 715.5(18) MHz
X. Yang, R. Z. Pearson, G. Scoles;
J. mol. Spectro.180, p 1-6, 1996
 The obtained rotational constants
from the microwave spectroscopy
are in good agreement with the
IR values.
Structural Analysis: Linear Model


IR spectroscopy determined rOC-HC = 2.615Å for OC---HCCCN complex
Yang, et. al., Chem. Phys. Lett., 204(12), p145-151, 1993.
Microwave spectroscopy determined rOC-HC = 2.577Å for OC---HCN
Goodwin, et. al., Chem. Phys., 87, p81-92, 1984.
b
r OC---HC
a
O
C
C
H
r c-c
r c.m.
b
C
C
N
a
Structural Analysis: Linear Model
How to find a distance that can best descrbe the complex?
Table-4: Various distances related to the linear model of OC---HCCCN and OC---DCCCN*
Molecular Species
rc.m. (Å)
rc-c (Å)
rOC-HC (Å)
OC---HCCCN
OC---HCCCN
O13C---HCCCN
OC---H13CCCN
OC---HC13CCN
OC---HCC13CN
OC---HCCC15N
OC---DCCCN
18
OC---DCCCN
O13C---DCCCN
OC---D13CCCN
OC---DC13CCN
OC---DCC13CN
OC---DCCC15N
18
6.2048
6.2361
6.1827
6.1687
6.1916
6.2179
6.2401
6.1443
6.1756
6.1222
N/A
6.1324
6.1588
6.1800
3.6610
3.6600
3.6613
3.6615
3.6611
3.6608
3.6609
3.6575
3.6564
3.6578
N/A
3.6576
3.6579
3.6574
*Kisiel’s STRFIT program gives us rOC-HC = 2.6018(5) Å
2.6035
2.6024
2.6038
2.6040
2.6036
2.6034
2.6034
2.6005
2.5994
2.6007
N/A
2.6006
2.6008
2.6004
Structural Analysis: Procession Model
 The description of the procession model:
E. J. Goodwin & A. C. Legon; Chem. Phys., 87, p81 – 92, 1984
H
rc-c
C
a
b
C
C
θ
O
a

C
rOC--HC
N
rc.m.
b



1 CO
1 HCCCN
2
I bb  r  I b 1  cos   I b
1  cos 2 
2
2
M CO  M HCCCN

M CO  M HCCCN
2
c.m.

Structural Analysis: Procession Model

Average effect of the procession around the a-axis



1
1 HCCCN
2
2
I bb  I bexp   rc2.m.  I CO
1

cos


I
1

cos

b
b
2
2


The geometry of the complex is determined by rc.m. and θ, , µ,
HCCCN
exp
I CO
,
I
,
I
b
b
b can be obtained from the experiment.
 can be obtained from the quadrupole coupling constant of 14N
 aa
1
  0 3 cos 2   1
2

 1  2  aa ( N )  


  arccos  

1
14

3

(
N
)


  0

14
1  2  aa (14N ) 
cos   
 1
3   0 (14N )

2
1
2


2
   d aa  d 0 
d   2
2 
  0   0  aa  2  aa 
Structural Analysis: Procession Model

For example, OC---HCCCN, aa(14N)=-4.20865(55)MHz, and the
0(14N) for free HCCCN is: 0(14N)=-4.31806(38)MHz, then:
OC---HCCCN:  =7.468(1)

For other isotopomers:
18OC---HCCCN:  =7.432(3)
O13C---HCCCN:  =7.473(1)
OC---H13CCCN:  =7.341(3)
OC---HC13CCN:  =7.473(1)
OC---HCC13CN:  =7.435(1)
OC---HCCC15N: N/A

  = 7.44(5) ↔  OC---HCN = 13-14
OC---DCCCN:  =7.31(4)
18OC---DCCCN: N/A
O13C---DCCCN:  =14.17(2)
OC---D13CCCN: N/A
OC---DC13CCN:  =6.05(6)
OC---DCC13CN:  =9.89(3)
OC---DCCC15N: N/A
Structural Analysis: Procession Model





Ibb is determined by the (θ, r2c.m.½) pair, how do we estimate θ?
Note that rc-c is almost isotropically invariant, and, (θ, rc-c) can also
be used to determine Ibb, i.e., Ibexp
Construct a set of (θ, rc-c) pairs from the main isotopomer and use
them to reproduce Ibbs for other isotopomers, and find the best
matched (θ, rc-c) pair to get the answer.
Examples:
18OC---HCCCN: Bexp  591.144MHz
B0 16  591.140MHz
0
B0 8  611.100MHz
 611.097MHz
O13C---HCCCN: Bexp
0
comparing with
18OC---HCN:
 ~ 15º
O13C---HCN:
 ~ 10º
The procession model does not work very well for HCCCN
isotopomers!
 ~ 0º - 90º (similar to the OC---HCN when use this model to
handle HCN isotopomers!)
Conclusion
1.
2.
3.
4.
5.
6.
The rotational spectra of the weakly bound van der
Waals complex dimers, including, OC---HCCCN, OC--DCCCN, and HCCCN---CO2 are observed.
All 13C (1.07%), 15N (0.37%), and 18O (0.205%)
isotopomers are found in natural abundance!
The obtained results are in good agreement with
previous studies
OC---HCCCN / OC---DCCCN is linear shaped. The
procession model is effective to describe this system.
The T-shaped HCCCN---CO2 has been observed. We
tried, but the linear shaped CO2---HCCCN was not
found yet!
Why the procession model failed to reproduce the
geometry of the OC---HCCCN complex when the
HCCCN subunit is substituted by 13C or 15N isotopes?
Future Plan
1.
Try to improve the quality of the data for OC---DCCCN by
observing low frequency transitions. (get the eqQ for D).
2.
Try to get the nuclear quadrupole coupling splittings due to the
13C of O13C-HCCCN. (can help us figure out  very accurately)
3.
Keep searching for the linear shaped CO2---HCCCN dimer.
4.
We already observed N2---HCCCN.
5.
We already observed HCCCN---HCCCN, HCCCN---DCCCN,
DCCCN---HCCCN, and DCCCN---DCCCN dimers (The low
frequency data will really help!).
6.
Searching for NO---HCCCN complex.
Acknowledgement

Andrea Meini
Department of Chemistry, Wesleyan University

Dr. Steven Shipman, Justin Neill, University of Virginia

Professor Wallace Pringle
Department of Chemistry, Wesleyan University

Union College, and Professor Brooks Pate, University
of Virginia.