STRUCTURES OF TWO ISOMERS OF NITROUS OXIDE TETRAMER FROM THEIR

INFRARED SPECTRA

J. Norooz Oliaee, F. Mivehvar, M. Dehghany,N. Moazzen-Ahmadi

Department of Physics and Astronomy University of Calgary

A.R.W. McKellarSteacie Institute for Molecular SciencesNational Research Council of Canada

Motivation• Weakly bound complexes provide a convenient starting point for a detailed understanding of different pathways that can be taken between the gas and condensed phases of matter.

•It is of considerable interest to determine the number of isomers for a cluster size and if and how geometrical choices made in the early stages of condensation influence the growth of larger clusters.

•Although it is expected that the number of isomers grows rapidly with cluster size, in many cases only a single isomer is observed experimentally.

The N2O dimer was also observed in the regions of the 1 band (Qian, Herrebout, Howard,

1997) and the 3 band (Oshima,

Matsumoto, Takami, Kuchitsu, 1988)

Summary of past works on N2O clusters

Non-polar dimer

Polar and non-polar isomers of (N2O)2

Wavenumber / cm-1

2226.0 2226.2 2226.4 2226.6 2226.8 2227.0

N2O - He

(N2O)2 nonpolar

(N2O)2 polar

* *

Dehghany, et al., JCP, 130, 044303 (2007).

Walker et al., JMS, 251, 153 (2008). MW spectrum

Non-polar isomer Polar isomer

Torsional combination band gives a frequency of 27.3 cm-1 for the out of plane torsional mode.

Wavenumber / cm-1

2249.2 2249.4 2249.6 2249.8 2250.0 2250.2

d

c

b

bandorigin

aSimulation based on the results by Hecker et al.(2003)

Results by NRC (2007)

Results by our group (2007)

Our simulation

Combination band involving the in-plane geared bend

N2O trimer

2232.5 2232.6 2232.7 2232.8 2232.9 2233.0 2233.1

observed

Wavenumber / cm-1

2163.2 2163.3 2163.4 2163.5 2163.6 2163.7 2163.8

observed

simulated

simulated

(14N2O)3

(15N2O)3

Three bands for (14N2O)3 in the 1 region of N2O monomer

Two bands for (14N2O)3 in the 3 region of N2O monomer (1280 cm-1)

Analogous bands for (15N2O)3

The barrel-shaped N2O trimer

Assignment is complicated by the lack of symmetry and a large number of possible combination bands (27) in the 1 region of N2O monomer.

Intermolecular frequency (in cm-1)   In-plane geared

bendTorsion of the

dimer unitTorsion of the

upper monomer Rocking of the upper monomer in a-c plane

(N2O)3 32.01? 30.26  44.54? 30.58?

(N2O)2 42.3 27.3  

Chemical Physics Letters 476 (2009) 143–146

Combination bands involving the intermolecular modes

N2O tetramer

14N2O tetramer with D2d symmetry

A parallel band showing no K structure.

It is centered at 2237.42 cm-1.

15N2O tetramer with D2d symmetry

The band due to (15N2O)4 does not show any K structure either.

It is centered at 2167.75 cm-1

c-type band can be well simulated using Cs symmetry.

A = 726.73 MHz B = 719.28 MHz C = 675.99 MHz

Mixed isotopomer (15N2O)3(14N2O)

1. The spectra above are consistent with a structure having D2d symmetry.

2 . The monomers are more or less parallel to the symmetry axis (close to perfect barrel shape) because of the absence of a perpendicular band sharing the same lower state parameters.

3. Tetramer is an oblate symmetric top with A = B = 753.14 MHz and C ~ 698 MHz.

Structure of (N2O)4 with D2d symmetry

4. Adjacent monomers have structure very similar to non-polar dimer.

5. Three structural parameters are required to define the geometry of the complex completely.

6. This is the same species that was observed by Miller and Pederson.

A second N2O tetramer band:this one is perpendicular, and located close to the trimer

band

The 15N15N16O isotopomer is shown here

For the normal isotope, this band is centered at

2232.209 cm-1

Wavenumber / cm-1

2162.7 2162.8 2162.9 2163.0 2163.1

observed

simulated trimer

simulated tetramer

N2O tetramer with S4 symmetry

Top view

Side view

symmetry axis

Side view

N2O tetramer with S4 symmetry1.Spectra are consistent with a structure having S4 symmetry.

2. Monomers are more or less perpendicular to

the symmetry axis, because of the absence of a

parallel band sharing the same lower state parameters.

3. Tetramer is a prolate symmetric top with

A = 747.52 MHz, B = C = 694.40 MHz (for (14N2O)4).

4. Diagonally opposite monomers have structure very

similar to nonpolar dimer with a dihedral angle of

about 30º. Adjacent monomers have

T- or L-shaped orientation.

5. Four structural parameters are required to define the geometry of the complex completely.

Experimental setup

TDL

Jet Trigger

Ref. Gas12 bit

DAQ Card

Timer Controller Card (CTR05)

LaserSweepTrigger

DAQTrigger

Gas Supply

Jet Signal

Jet Controller (Iota One)

Jet Controller

IR DetectorsTDL Controller (L5830)

Etalon

Monochromator

Supersonic jet apparatus with a tunable diode laser probe