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Spectroscopy of He-, Ne-, and Ar - C2D2 complexes
Mojtaba Rezaei, Nasser Moazzen-AhmadiDepartment of Physics and Astronomy
University of Calgary
A.R.W. McKellar
National Research Council of Canada Berta Fernández
University of Santiago de Compostela
David Farrelly
Utah State University
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TDL
Jet Trigger
Ref. Gas12 bit
DAQ Card
Timer Controller Card (CTR05)
LaserSweep
Trigger
DAQTrigger
Gas Supply
Jet Signal
Jet Controller (Iota One)
Jet Controller
IR DetectorsTDL Controller (L5830)
Monochromator
pulsed supersonic jet / tunable diode laserapparatus at The University of Calgary
Etalon
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Mol. Phys. 77, 111 (1992)
Experimental spectra of helium – acetylene have never been published
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J. Chem. Phys. 102, 8385 (1995)
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This is the best He-HCCH potential currently available,
so we asked Berta Fernández to calculate energy levels for He-HCCH and He-DCCD.
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En
erg
y /
cm-1
-8
-6
-4
-2
0
0
1
1 e 1 f
0
01
1
11
2
2
22
3 3
3
3
4
4
44
He – C2D2 energy levels calculated by Fernández & Farrelly from the Munteneau & Fernández CCSD(T) potential
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Coriolis model. Used by Brian Howard for Rg – SiH4 complexes and by the Köln group for Rg – CH4. For the moment, we are concerned only with j = 0 and 1 levels, where j is the DCCD rotation. There is one stack of rotational levels for j = 0, denoted 0 σe. There are three stacks for j = 1, denoted 1 f, 1 e, and 1 σe.
E(0 σe) = B(0) J(J + 1) – D(0) [J(J + 1)]2
E(1 f) = Evr + + B(1) J(J + 1) – D(1) [J(J + 1)]2
E(1 σe) = Evr – + B(1σ) J(J + 1) – D(1) [J(J + 1)]2
connected by off-diagonal Coriolis coupling: [J(J +1)]1/2
E(1 e) = Evr + + B(1) J(J + 1) – D(1) [J(J + 1)]2 This model represents the ab initio levels fairly well.
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Wavenumber / cm-1
2440.5 2441.0 2441.5 2442.0 2442.5
P(1)
Q(J)
R(0)
C2D2 R(0) line(C2D2)2 lines
simulated Coriolis model fit
observed spectrum
simulated from ab initio levels
R(J) and P(J)
He – C2D2
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Wavenumber / cm-1
2440.75 2440.80 2440.85 2440.90 2440.95
simulated Coriolis model fit
observed spectrum
simulated from ab initio levels
C2D2 R(0) line(C2D2)2 lines
R(2)R(3),P(3)
R(1)
R(0)R(4)
P(2)P(4)
P(2) P(3)
R(0)
R(1)
R(2)
R(3)
R(4) P(4)
He – C2D2
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He – C2H2 He – C2D2
Theory Moszynski
et al.
Theory Munteanu & Fernández
Theory Munteanu & Fernández
Experiment
B(0) 0.25307 0.24470 0.24171 0.24173
D(0) 0.00042 0.00042 0.00057 0.00015
Evr 2.5608 2.4461 1.8053 1.8383 b
B(1σ) 0.22817 0.23153 0.22972 0.22856
B(1) 0.26605 0.24814 0.24974 0.25132
-0.2743 +0.3282 +0.3413 +0.2071
1/2 0.45476 0.47384 0.46639 0.48063
D(1) 0.00046 0.00015 0.00035 -0.00001
j* 0.865 0.958 0.953 0.985
j* is dimensionless; j* = 1 in the free rotation limit
Coriolis model parameters (cm-1)
positive means linear negative means T-shaped zero means free rotation
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-0.4 -0.2 0.0 0.2 0.4 0.6
P(1)
Q(J)
1 2
3
4
Wavenumber / cm-1-0.14 -0.12 -0.10 -0.08 -0.06
P(2)
R(2)
R(3)R(4)
P(3)
P(4)R(5) R(0)R(1)
This is our predicted He – HCCH spectrum for the j = 1 – 0 region, near R(0) of the HCCH 3 band
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Microwave spectra of He – acetylene have never been reported. We predict R(0) for the j = 0 stack of He – C2D2 to lie around 14475
MHz.
So far, our He – C2D2 analysis is limited to the j = 1 0 region. There is also a j = 0 1 spectrum, but in our current data it is mostly obscured by (C2D2)2 transitions.
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Wavenumber / cm-1
2440.6 2440.8 2441.0 2441.2 2441.4
observed
simulated
Q(J)
R(J)P(J)
P(1)R'(0)
(C2D2)2
C2D2
R(0)
Ne – C2D2
j = 1 0 spectrum, near C2D2 R(0)
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Ne – C2D2 He – C2D2
B(0) 0.08907 0.24173
Evr 1.6739 1.8383
B(1σ) 0.08501 0.22856
B(1) 0.09242 0.25132
+0.1233 +0.2071
1/2 0.1653 0.48063
j* 0.907 0.985
Coriolis model parameters (cm-1)
negative means T-shapedpositive means linear
includes j = 1 energy and vibrational shift
j* is dimensionlessj* = 1 in free rotation limit
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Ne – C2D2
We think the correct assignment here may be:
1 state3-2 10999.15184-3 16015.7988
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2442.2 2442.4 2442.6 2442.8
C2D2
R(1)
Wavenumber / cm-12443.6 2443.8 2444.0 2444.2
C2D2
R(2)
Ne – C2D2
j = 2 1 spectrum, near C2D2 R(1)j = 3 2 spectrum, near C2D2 R(2)
not assigned yet
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Wavenumber / cm-1
2439.8 2440.0 2440.2 2440.4 2440.6 2440.8
observed
simulated
Ar – C2D2
K = 1 0 subband
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Wavenumber / cm-1
2441.6 2441.8 2442.0 2442.2
observed
simulated
Ar – C2D2
K = 2 1 subband
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Col 1 vs Ar-C2D2plt3-1
Wavenumber / cm-1
2442.8 2443.0 2443.2 2443.4
observed
simulated
Ar – C2D2
part of bending combination band, v2 = 1 0, K = 0 0plus other unassigned structure
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Conclusions• First assignment for He – acetylene. Fernández potential works fairly well, but the real complex is even closer to the free rotation limit.
• Ne – C2D2 is also close to the free rotor limit and
hence tricky to assign, especially for j > 1. Data are incomplete: we need spectra in the j = 0 1 region.
• Ar – C2D2 is more like a ‘normal’ molecule and
relatively easy to assign. Data also incomplete. Asymmetric rotor fit is possible, but not very good. Better to treat each ‘state’ (v, K) separately (similar to Ar – CO).