Fourier transform microwave
spectra of Ne-(CH3)2O and Ar-(CH3)2O
Yoshiyuki Kawashima, Yasutoshi Morita,
Nobuyuki Ohashi*, and Eizi Hirota＋
Kanagawa Institute of Technology,
Kanazawa University*, and
The Graduate University for Advanced Studies＋
(the 60th spectroscopy conference on 23/June/2005)
Background
Molecular Beam + FTMW spectroscopy:
high resolution and high sensitivity
Observation of van der Waals complexes
determination of rotational, centrifugal distortion, and
hyperfine coupling constants and also of approximate
structure parameters of the complexes.
It is probably because most of intra-complex motions are
of large amplitude and thus are not easy to handle. So
far, only a few simplest types of complexes have been
investigated in detail in this respect.
Heterodimer consisting of a rare gas
atom and a C2V molecule
Ar-SO2:
Microwave transitions observed by DeLeon et al. (1980)
Extended observation by Coudert et al. (1991)
Analysis using a generalized IAM formalism (Coudert
and Hougen, 1988)
Schäfer reivestigated by the Coriolis interaction between
the internal motion and the overall rotation (2001).
Rcm = 3.675 Å and the tunneling splitting is 980 MHz.
Purpose of the present study
The present study focused attention to two complexes:
Ne-DME and Ar-DME. These complexes are quite
simple in structure, but the motion of Rg in the
complex do not seem to have been properly analyzed
in previous publications.
We have expected that addition of new experimental
data, which are much more complete and precise
than available, would open for us an access to the
potential surfaces of intra-complex large-amplitude
motions.
Rg-DME
a-type
c-type
(splitting)
transition transitions
References
Ne-DME
25 (1600 MHz)
(1) A. Maris et al., J. Chem. Phys. 118 (2003) 1649
Ar-DME
50
(2 MHz)
(2) P. Ottaviani et al., Chem. Phys. Lett. 361 (2002) 341
Kr-DME
30
(0.4 MHz) (3) B. Velino et al., J. Chem. Phys. 108 (2004) 4224
Xe-DME
11
no splitting
8
(0.2 MHz) (4) W. Caminati et al., Chem. Phys. Lett. 392 (2004) 1
Purpose
1. Observation of the a-type transitions for Ne-DME and
Ar-DME
2. Analysis the observed frequencies considering the
Coriolis interaction
Tunneling potential curve of Ne-DME
Ne
Rc.m.=3.48Å
E
O
C
C
α =115°
B = 0.19 kJ mol-1
1
v = 1+
0
v= +
0
ｰ115°
0°
+115°
α
(12) = σ(yz)
E
y
y
C2
C1
C1
Rg
z
a0
Rg
C2
O
O
(12)’ = C2z
E’ = σ(zx)
y
y
O
a0
C2
C1
z
a0
z
Rg
C1
C2
a0
O
z
Rg
Symmetry operations of Rg-DME
Character table of G4
selection rule and spin weight
G4
C2v
E
E
A1
A2
B1
B2
1
1
1
1
(12)’
E’
(12)
C2(z) σv(zx) σv(yz)
1
1
-1
-1
1
-1
1
-1
1
-1
-1
1
μz
Jz
μx J y
μy J x
|s＞| ee＞, |a＞| oe＞
|s＞| eo＞, |a＞| oo＞
|s＞| oo＞, |a＞| eo＞
|s＞| oe＞, |a＞| ee＞
μz ≠ 0 (a-type transition)
|s＞|ee＞↔|s＞|eo＞,
|a＞|oo＞↔|a＞|oe＞ (A1↔ A2)
|s＞|oo＞↔|s＞|oe＞, |a＞|ee＞↔|a＞|eo＞ (B1↔ B2)
μy ≠ 0 (c-type transition)
|s＞|ee＞↔|a＞|oe＞
|s＞|oo＞↔|a＞|eo＞
(A1↔ A2)
(B1↔ B2)
Spin weight
A : B = 28 : 36
Character table of G36 for Rg-DME
Class
G36
E
(123)(456)
(14)(26)(35)(ab)*
(123)(465)
(132)
142635)(ab)*
(14)(25)(36)(ab)
(142536)(ab)
(23)(56)*
(C3v)2
EE
2EC3
3Eσv
2C3E
4C32
6C3σv
3σvE
6σvC3
9σv2
G36
(C3v)2
A1
A1A1
1
1
1
1
1
1
1
1
1
B1
A2A1
1
1
1
1
1
1
-1
-1
-1
A2
A1A2
1
1
-1
1
1
-1
1
1
-1
B2
A2A2
1
1
-1
1
1
-1
-1
-1
1
E1
EA1
2
2
2
-1
-1
-1
0
0
0
E2
EA2
2
2
-2
-1
-1
1
0
0
0
E3
A1E
2
-1
0
2
-1
0
2
-1
0
E4
A2E
2
-1
0
2
-1
0
-2
1
0
G
EE
4
-2
0
-2
1
0
0
0
0
Experimental
1% mixture gas of DME diluted with Ne or Ar
Backing pressure: 2 ～ 3 atm
Co-adds: 20～1000 shots
Spectral region: 4～25 GHz
Introducing LabVIEW
Multifunction I/O: slow A/D converter
Timing I/O: timing pulses for switches and nozzle driver
Digitizer : 64MS/s and 14 bit
The frequency resolution is 0.4 kHz.
Ar-DME
40 a-type transitions
22 c-type transitions
in the region 4 – 25 GHz
Spin weight
Measured by Prof.Ogata
Q-branch lines:
Intensity ratio of B/A
= 1.34 (19)
9619.0921 MHz
A1 313(a) ← A2 212(a)
Ar-DME
a-type
9618.70
9618.90
9619.10
10844.3973 MHz
A2 110(a) ← A1 000(s)
9619.30
9619.50
DME－Ar
c-type
theoretical value = 1.286
10844.00
10844.20
10844.40
10844.60
10844.80
c-type transitions of Ar-DME
①
①17305.5089 MHｚ
(G1 533 ← G2 625)
③17307.1361 MHｚ
(G1 533 ← G2 625)
③
④17307.1732 MHｚ
②17305.5382 MHｚ
(B1 533 ← B2 625)
(E4 533 ← E4 625)
(A1 533 ← A2 625)
④
②
17305.0
17305.2
17305.4
⑤16999.0441 MHｚ
(G1 532 ← G2 624)
(B2 532 ← B1 624)
17305.6
17305.8
17306.0
17306.6
17306.8
17307.0
⑤
17307.2
17307.4
17307.6
17000.7
17000.9
17001.1
⑦
⑦17000.6315 MHｚ
(G2 532 ← G1 624)
(A2 532 ← A1 624)
⑥16999.0743 MHｚ
(E4 532 ← E4 624)
⑥
16998.5
16998.7
16998.9
16999.1
16999.3
16999.5
17000.1
17000.3
17000.5
① 13245.1709 MHz
②
（A2 432 ← A1 331）
（B2 432 ← B1 331）
DME－Ar
a-type
transition
③
② 13245.2432 MHz
（G1 432 ← G1 331）
（G2 432 ← G2 331）
③ 13245.4617 MHz
（G1 431 ← G1 330）
（G2 431 ← G2 330）
④
①
④ 13245.5281 MHz
⑤
（A1 431 ← A2 330）
432 ← 331
431 ← 330
⑤ 13245.5369 MHz
（B1 431 ← B2 330）
13244.8
13244.9
13245
13245.1
13245.2
13245.3
13245.4
13245.5
13245.6
13245.7
13245.8
13245.9
／ＭＨｚ
Rg-DME: effective Hamiltonian
Symmetric
antisymmetric
-1/2Δ + RzzsJz2 + RxxsJx2 +
iQxJx + Ryz(JyJz + JzJy)
RyysJy2 + centrifugal terms
+ centrifugal terms
-iQxJx + Ryz(JyJz + JzJy)
1/2Δ + RzzaJz2 + RxxaJx2 +
+ centrifugal terms
RyyaJy2 + centrifugal terms
Molecular constants of Ar-DME
This work
A
B
/MHz
/MHz
C /MHz
ΔJ /MHz
ΔJK /MHz
ΔK /MHz
δJ /kHz
δK /kHz
ΔE inv /MHz
q int /MHz
V 3 /cm-1
N
σ
a)
/MHz
9081.9073(9)
1761.77338(15)
1551.40106(11)
0.0101841(19)
0.190644(34)
-0.15770(26)
-1.2851(10)
-0.43259(35)
1.0034(10)
0.02267(26)
Previous studya)
9081.8992(7)
1761.7705(2)
1551.3994(2)
0.010117(4)
0.19041(4)
-0.1546(2)
-1.2898(3)
-0.4356(4)
0.9980(9)
558(1)
231
0.0036
100
0.09
Centrifugal distortion constants were used as S reduction
Ne-DME
No spectral data for Ne-DME in the
region below 60 GHz
10220.5100 MHz
Ne-DME
B1 202(a) ← B2 101(a)
a-type
18 a-type and 18 c-type transitions
assigned by taking “combination
difference”
10220.10
10220.30
10220.50
10220.70
10220.90
Inversion splittings
c-type transition: 1300~1600 MHz
11309.7603 MHz
B2 110(s) ← B1 000(a)
c-type
a-type transition: 1~38 MHz
Internal splittings are almost constant,
0.080 MHz. These splittings were
accounted for the change of inversion
splitting by CH3 internal rotation.
Ne- DME
11309.35
11309.55
11309.75
11309.95
11310.15
/ MHz
Molecular constants of Ne-DME
This work
A /MHz
B /MHz
C /MHz
ΔJ /MHz
ΔJK /MHz
ΔK /MHz
δJ /MHz
δK /MHz
ΔE inv/MHz
q inv /MHz
ΔE int.+inv./MHz
N
σ
a)
/MHz
Previous studya)
9281.138(5)
2825.3357(14)
2305.0614(26)
0.05928(8)
2.2697(14)
-1.7056(23)
-0.01257(6)
-0.00751(26)
817.8164(40)
66.22(21)
0.0257(5)
9281.9(3)
2823.7(2)
2302.6(3)
0.052(1)
2.245(7)
-1.62(3)
-0.0152(3)
-0.01567(4)
807.2(9)
62
0.0062
50
0.18
Centrifugal distortion constants were used as S reduction
Summary
1. The present study has completed the observations of all
the possible types of rotational spectra for Ne-DME
and Ar-DME.
2. The observed transition frequencies have been
analyzed in detail. Some of the transitions observed by
the present study exhibited additional splittings, which
were interpreted as due to internal rotation of the
methyl groups in DME.
3. For Ar-DME the splittings appeared only in high-K
transitions, yielding the V3 potential barrier to be 558
(1) cm-1, whereas those observed for Ne-DME were
ascribed to the effects of CH3 internal rotation on the
inversion splitting.
Acknowlegdements
We thank Prof. T. Ogata of Shizuoka
University for providing us with his data on
relative intensity measurements.