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C. T. Dewberry, G. S. Grubbs II and S. A. Cooke

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1 C. T. Dewberry, G. S. Grubbs II and S. A. Cooke
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

2 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 1-iodopropane. (M. Fujitake and M. Hayashi 127 (1988) 112)

3 Forbidden transitions
Require: Near degeneracy. Energy levels involved must be connected via a component of the nuclear quadrupole coupling tensor.

4 Trans-1-iodoperfluoropropane
Drawn with PMIFST, free from the PROSPE website

5 Experimental methods Search Accelerated Correct Intensity Fourier Transform Microwave (SACI-FTMW) Spectroscopy. Smitty Grubbs Talk WF13 RSI 78 (2007)

6 Experimental methods Fourier Transform Radiofrequency FTRF Spectroscopy. Chris Dewberry Talk MH13 JMS 242 (2007) 39

7 Experimental methods Traditional Balle-Flygare-type FTMW Spectroscopy
Circuit design follows that of Jens Uwe Grabow CP 342 (2007) 71

8 Results

9 Results

10 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.

11 Spectroscopic Parameters of trans-1-iodoperfluoropropane

12 Forbidden transitions
JK-1,K+1F : 16 9,7 31/2 ← 13 10, 4 29/2

13 Forbidden transitions

14 Forbidden transitions
My .int file:

15 The .egy file

16 The 16 9,7 31/2 ← 13 10, 4 29/2 Transition Pmix is for 16 9,7 31/2 and for 13 10, 4 29/2 Find that the 15 9,6 29/2 level is just 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 > = 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.

17 Similar arguments prevail for all of the forbidden transitions observed.

18 The 14 4,10 23/2 ← 12 5, 7 21/2 Transition

19 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.

20 Acknowledgements Profs. Mike Gerry, Jon Hougen and Stew Novick for insightful comments. $$ NSF CHE


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