Transcript cooke1-09.ppt

FORBIDDEN TRANSITIONS IN THE VERY RICH
PURE ROTATIONAL SPECTRUM OF
TRANS-1-IODOPERFLUOROPROPANE
C. T. Dewberry, G. S. Grubbs II and S. A.
Cooke
Department of Chemistry, University of
North Texas, Denton, TX
Background
• In 1957 Javan proposes the use of D J = +3 or +2
transitions in relation to stimulated emission.
(PR 107
(1957) 1579)
• In 1966 Oka observes a D J = +3 transition in ethyl iodide.
(JCP 45 (1966) 752)
• A handful of molecules have been studied in which
forbidden transitions are observable including 1iodopropane. (M. Fujitake and M. Hayashi 127 (1988) 112)
Forbidden transitions
• Require:
– Near degeneracy.
– Energy levels involved must be connected via a
component of the nuclear quadrupole coupling
tensor.
Trans-1-iodoperfluoropropane
Drawn with PMIFST, free from the PROSPE website
Experimental methods
• Search Accelerated Correct
Intensity Fourier Transform
Microwave (SACI-FTMW)
Spectroscopy.
Smitty Grubbs
Talk WF13
RSI 78 (2007) 096106
Experimental methods
• Fourier Transform Radiofrequency FTRF Spectroscopy.
Chris Dewberry
Talk MH13
JMS 242 (2007) 39
Experimental methods
• Traditional Balle-Flygare-type FTMW Spectroscopy
Circuit design follows that of Jens Uwe Grabow
CP 342 (2007) 71
Results
Results
Results
• 776 transitions for the parent between 1 and 17 GHz.
Energy levels covering J = 1 to 50. Both a- and b- types,
Q and R branches.
• 32, 58 and 51 transitions for the carbon-13 C(1), C(2)
and C(3) species, respectively.
• Watson S Hamiltonian (κ = -0.97), Ir representation.
Use Herb Picketts SPFIT/SPCAT.
Spectroscopic Parameters of trans-1-iodoperfluoropropane
Forbidden transitions
JK-1,K+1F : 16 9,7 31/2 ← 13 10, 4
29/2
Forbidden transitions
Forbidden transitions
My .int file:
pfip fit
0123
00001
1 1.5
2 1.0
1314.
00
99
-6.5 -6.5
13.0
4.0
The .egy file
The 16 9,7 31/2 ← 13 10, 4 29/2 Transition
•
Pmix is 0.99908 for 16 9,7 31/2 and 0.96887 for 13 10, 4 29/2
•
Find that the 15 9,6 29/2 level is just 161.3 MHz above the 13 10, 4 29/2 level.
H. P. Benz et al.
JMS 21 (1966) 156
•A Fortran 77 code shows a non-zero matrix element
< 13 10, 4 29/2 | HQ | 15 9,6 29/2 > = -27.585 MHz.
•The magnitude of this matrix element scales only with the manitude of χab .
•16 9,7 31/2 ← 15 9, 6 29/2 is an allowed a-type transition.
Similar arguments prevail for all of the forbidden transitions
observed.
The 14 4,10 23/2 ← 12 5, 7 21/2 Transition
Conclusions
• First rotational spectroscopy on trans-1-iodoperfluoropropane.
• Numerous dipole forbidden transitions observed. (Some were very
strong).
• Rationalization appeals to near degeneracies between energy levels that
are linked via χab .
• Possible candidate for use in stimulated emission experiments.
• SPFIT/SPCAT calculations show that the strength and number of dipole
forbidden transitions can be enhanced by increasing the magnitude of χab
, and/or increasing the number of near degeneracies.
• Studies initiated on the butane and pentane analogs.
Acknowledgements
• Profs. Mike Gerry, Jon Hougen and Stew
Novick for insightful comments.
• $$ NSF CHE-0820833