Spectroscopy of NCNCS at the Canadian Light Source: the far-infrared spectrum of the ν 7 region...

Spectroscopy of NCNCS at the Canadian Light Source:

the far-infrared spectrum of the ν7 region from 60-140 cm-1

(and beyond…)Dennis W. Tokaryk, Stephen C. Ross

Department of Physics and Centre for Laser, Atomic, and Molecular Sciences

University of New Brunswick, Fredericton, NB Canada

Brenda Winnewisser, Manfred Winnewisser, F. C. De Lucia

Department of Physics, The Ohio State University, Columbus, OH USA

Brant E. BillinghurstCanadian Light Source, Inc., Saskatoon, SK Canada

69th International Symposium on Molecular Spectroscopy Champaign-Urbana, IL USA June 19, 2014


Background: the energy-momentum map ofNCNCS presented in the previous talkhas been calculated, not measured.

Genera

te p

ara

mete

rs d

esc

ribin

g t

he

pote

nti

al by fi

ttin

g B

eff,

Deff f

rom

each

ro

tati

onal vb/K

a s

eri

es.

Calc

ula

te e

nerg

ies

from

fitt

ed

pote

nti

al


Objective: to measure the (vb, J=Ka) levels on this maprelative to one another using the far-infrared

rotation-vibration spectraobtained at the CLS


Objective: to locate the (vb, J=Ka) levels on this maprelative to one another using the far-infrared

rotation-vibration spectraobtained at the CLS

b-type sub-bands

a-type sub-bands


Phase 1: the spectrum of the ν7 low-frequency high-amplitude bending mode



v b 1

-0 K

a =

0

An

Inte

ract

ive

Lo

om

is-w

oo

d P

acka

ge

for

Sp

ectr

al A

ssig

nm

ent

in Ig

or

Pro

.N

eese

, C. F

.F

ifty-

sixt

h O

hio

Sta

te U

nive

rsity

Inte

rnat

iona

l Sym

posi

um o

n M

olec

ular

Spe

ctro

scop

yC

olum

bus,

Ohi

o, J

une

11-1

5, 2

001.



Mask

Data

Correlation spectrum



Up to

Ka = 10

Ka = 10

Ka = 12

Ka = 12

Origins of 68 a-type sub-bands of the ν7 spectrumdetermined in ~1.5 hours with the correlation

procedure!

But no b-type sub-bands were found… : (


Phase 2: the spectrum of the ν3 hybrid band stretching mode

PGOPHER, a Program for Simulating Rotational Structure, C. M. Western, University of Bristol, http://pgopher.chm.bris.ac.uk

a-type sub-bands

b-type sub-bandsb-type sub-bands

http://pgopher.chm.bris.ac.uk/



Ka

Ka

Ka+1

Ka-1

ν3=1

ν3=0

v 3

Ka =

6

a-ty

pe

• identify a-type sub-bands the hard way fora given value of Ka.

• calculate term energies in the ν3 level.

• create mask spectrum from upper state termenergies and calculated levels for v=0, Ka ±1.

• correlate the mask spectrum with the data.



Ka’-Ka’’

3-2

4-3 5-

46-

57-

6

6-7 5-6

4-5

3-4

7-8


The energy-momentum map so far…

Up to

Ka = 10

Ka = 10

Ka = 12

Ka = 12

The relative energy of all states connected by arrowsare now known…. : )

But the stacks with Ka=0and Ka=1 still float relativeto the others… : (


Where to next?

FAAAST Rotational spectrum: correlator failed to turn up the b-type sub-bands that would connect Ka 1-0 and 2-1.

Hybrid bands in 400-460 cm-1 range: lots of b-type Q-branches among the a-type spectra. The data potentially contain the two missing connections needed to complete the energy-momentum map.


Conclusions

A directly measured energy-momentum map for the bending mode of NCNCS is nearly complete!

The potential function for the bending motion, obtained by fitting only Beff and Deff constants from pure rotational data with Stephen Ross’ Generalized Semi-Rigid Bender program, predicted vibrational level positions relative to one another to within ~2 cm-1 (for the levels I’ve

checked – not an exhaustive list). The physics that underlies quantum monodromy imprints itself on the large-amplitude bending motion (and a wide selection of other physical properties) of molecules…

… and the GSRB Hamiltonian captures that physics very nicely.

(DWT thanks Damien Forthomme and Colin Sonnichsen for help with the experiments, and NSERC for research funds.)

1 2 3 4 5

Welcome to the world where vibration and rotation can not be separated and the

eigenfunctions can not be factored: Dynamics of large amplitude motion

Quantum monodromy

in a Champagne bottle potential function

Spectroscopy of NCNCS at the Canadian Light Source: the far-infrared spectrum of the ν 7 region...

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