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

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

Mol. Phys. 77, 111 (1992)

Experimental spectra of helium – acetylene have never been published

J. Chem. Phys. 102, 8385 (1995)

This is the best He-HCCH potential currently available,

so we asked Berta Fernández to calculate energy levels for He-HCCH and He-DCCD.

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

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.

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

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

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

-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

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.

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)

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

Ne – C2D2

We think the correct assignment here may be:

1 state3-2 10999.15184-3 16015.7988

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

Wavenumber / cm-1

2439.8 2440.0 2440.2 2440.4 2440.6 2440.8

observed

simulated

Ar – C2D2

K = 1 0 subband

Wavenumber / cm-1

2441.6 2441.8 2442.0 2442.2

observed

simulated

Ar – C2D2

K = 2 1 subband

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

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).