The Rotational Spectra of Cyclohexene Oxide and Its Argon van der Waals Complex DANIEL J. FROHMAN, STEWART E. NOVICK AND WALLACE C. PRINGLE Wesleyan University June 19, 2012 TH05

Motivation Cyclohexene oxide is one molecule in a series of similar small ring species Similar species are cyclopentene oxide (CPO) and cyclopentanone Argon vdW complexes of rings are simple models of the effects influencing weak bonding (different substituent groups and ring motions (bending, puckering, etc…) 2 Minei, A. J,. et al. J. Phys. Chem. A

Cyclohexene Oxide Previously studied 1,2, A, B, & C and some centrifugal distortion terms determined for parent and 18 O and 13 C isotopologues 2 Unlike cyclopentene oxide has no plane of symmetry, is very asymmetric, and so each carbon is unique 6 th carbon kinks ring near the rear μ a = (6), μ b = 0.18 (8), μ c = 1.52 (1) Debye, meaning all 3 types of transitions, a, b, and c observable but b types will be weak 1 All species observed in natural abundance 3 1.) Ikeda, T. K., Roger; Curl Jr., R.F. J. Mol. Spec. 1972, ) Sanchez, R. B., Susana; Lopez, Juan C.; Alonso, Jose L. J. Mol. Struct. 2006, Images from PMIFST

New Results This work refined the rotational constants and added the remaining quartic C.D. terms through observation of many more transitions for the parent and its 13 C and 18 O isotopologues Newly reported data for the 17 O isotopologue which displays hyperfine structure via electric quadrupole splitting Substitution structure from fitting isotopologues of use for predicting the Ar vdW complex spectra Fit with I r representation and Watson A Hamiltonian with Pickett Suite of software, SPCAT and SPFIT 4 abc CαCα (1) (2) (3) C α' (2)0.830 (2) (4) CβCβ (8) (1) (5) C β' (4)1.511 (1)0.000 (71) CγCγ (1) (2)0.471 (3) C γ' (1)0.567 (3) (10) O (from 18 O)1.488 (1)0.029 (51)0.716 (2) O (from 17 O) (1)0.030(50)0.716 (2) Pickett, H. M. J. Chem. Phys. 1991,

17 O Isotopologue Very low natural abundance 1, 0.038%, compared to 0.205% for 18 O or 1.07% for 13 C Nuclear spin, I = 5/2 Very few 17 O species studied in microwave and most appear to be diatomic 2 or triatomic A similar 17 O species observed is oxirane or ethylene oxide, the most simple epoxide 3 Quadrupole coupling constants of C 6 H 10 O and oxirane are in agreement 5 1.) 2.) Cooke, S. et al. Phys. Chem. Chem. Phys ) Creswell, R. A.; Schwendeman., R.H. Chem. Phys. Lett. 1974, Sourceχ aa \ MHzχ bb \ MHzχ cc \ MHz Oxirane (G09) † Oxirane Expt CHO (G09)*† CHO Expt.* * Results transformed into PAS of oxirane † MP2/aug-cc-pVTZ

Sample 17 O transition image from FTMW++ 6

Rotational Constants of C 6 H 10 O 7 C 6 H 10 O 13 C α C 5 H 10 O 13 C α' C 5 H 10 O 13 C β C 5 H 10 O 13 C β' C 5 H 10 O 13 C γ C 5 H 10 O 13 C γ' C 5 H 10 O A (MHz) (18) (39) (59) (26) (22) (31) (32) B (MHz) (18) (24) (36) (16) (13) (19) (19) C (MHz) (17) (37) (56) (25) (20) (29) (30) Δ J (kHz) (50)0.438 (12)0.410 (18)0.405 (8)0.415 (7)0.422 (10)0.398 (10) Δ JK (kHz) (62)[-0.589] Δ K (kHz) (50)[ ] δ J (kHz) (13)[0.1243] δ K (kHz) (32)[0.1598] N (lines) 5314 σ (kHz)

Rotational Constants of C 6 H 10 O 8 C 6 H 10 OC 6 H O C 6 H O A (MHz) (18) (62) (19) B (MHz) (18) (41) (19) C (MHz) (17) (69) (23) Δ J (kHz) (50)0.437 (22) (78) Δ JK (kHz) (62)[-0.589] Δ K (kHz) (50)[ ] δ J (kHz) (13)[0.1243] δ K (kHz) (32)[0.1598] χ aa (MHz) n/a (49) χ bb (MHz) n/a (37) χ cc (MHz) n/a (37) N (lines) σ (kHz)

Argon Cyclohexene Oxide vdW complex of Ar and C 6 H 10 O along with its 13 C isotopologues fit Position of Ar determined in 4 ways: r e structure, r 0 structure, r s from Kraitchman substitution structure, and mixed r 0, r s, r e structure Difficult to determine Ar position, 8 possibilities and lines from 6 unique carbons a, b, and c type transitions observed for parent and a and b for the 13 C isotopologues Unlike in HCl C 6 H 10 O complex 1, the Ar avoids the negatively charged oxygen lone pair electrons and like a Lewis base, is nearest to the most positive part of the ring, the H α and H α’ Unlike in Ar CPO, lack of symmetry plane contributes to Ar favoring H α’ over H α position Argon is Å away from H α’ which is larger than the vdW radii sum, 2.97 Å 2,3 9 1.) Sanchez, R. B., Susana; Lopez, Juan C.; Alonso, Jose L. J. Mol. Struct. 2006, ) Bondi, A. J. Phys. Chem. 1964, ) Rowland, R. S. T., Robin J. Phys. Chem. 1996,

Ar Position Expectation is for Ar to be near polarizable oxygen lone pairs or near the polar C-O bonds Instead Ar is essentially right over the LUMO, behaving like a Lewis Base 1 Small difference in r e and r 0 Ar position relative to LUMO due to vibrational averaging of ring motions and vdW stretch 10 1.) J. Chem. Phys pg 193 Harris, Stephen J.; Novick, Stewart E.; Klemperer, William; Falconer, Warren E.

Fitting of Argon C 6 H 10 O A-type transitions primarily depend on B & C, give easily recognizable patterns Ab initio Ar position did not reproduce spectral patterns well due to B and C constants ArCPO method  better predictions for B & C constants  matching of predicted & experimental a-type transitions easier, patterns more recognizable 11 abc CαCα (5)0.700 (2) (4) C α' (5)0.711 (2) (4) CβCβ (5)0.697 (2) (4) C β' (5)0.694 (2) (4) CγCγ (5)0.729 (2) (4) C γ' (5)0.707 (2) (4) Ar (r 0 ) (5)0.706 (2) (4) Ar (r s ) (5)0.706 (2) (4) Ar (r e, ab initio) ArCPO Ar (r 0, r e, r s ) (2)0.706 (1) (14) Ar positions in monomer PAS

Rotational Constants of ArC 6 H 10 O 12 ArC 6 H 10 OAr 13 C α C 5 H 10 OAr 13 C α' C 5 H 10 OAr 13 C β C 5 H 10 OAr 13 C β' C 5 H 10 OAr 13 C γ C 5 H 10 OAr 13 C γ' C 5 H 10 O A (MHz) (15) (17) (13) (28) (26) (17) (14) B (MHz) (78) (12) (10) (19) (18) (12) (10) C (MHz) (84) (11) (9) (18) (16) (11) (9) Δ J (kHz) (35) (90) (71) (14) (13) (92) (72) Δ JK (kHz) (21)7.186 (19)7.224 (15)7.258 (30)7.414 (28)7.029 (19)7.169 (15) Δ K (kHz) (12)[-7.643] δ J (kHz) (18)[ ] δ K (kHz) (29)[-1.122] N (lines) σ (kHz)

Conclusion Rotational constants for the monomer and its 13 C and 18 O isotopologues refined and added to First time reported 17 O isotopologue, adds to small number of 17 O species studied via microwave reported Argon vdW complex and its 13 C isotopologues found Argon position determined through multiple methods, located away from oxygen and is closer to the more positive H α and H α’ near front of the ring Ar distance to the closest atom H α’ is Å, which is larger than the vdW radii sum 2.97 Å 1, ) Bondi, A. J. Phys. Chem. 1964, ) Rowland, R. S. T., Robin J. Phys. Chem. 1996,

Acknowledgements Novick & Pringle research group members for advice 14

Acknowledgements Novick & Pringle research group members for advice 15 constantC 6 H 10 O 13 C α C 5 H 10 O 13 C α' C 5 H 10 O 13 C β C 5 H 10 O 13 C β' C 5 H 10 O 13 C γ C 5 H 10 O 13 C γ' C 5 H 10 OC 6 H OC 6 H O Ia Ib Ic P aa P bb P cc constantArC 6 H 10 OAr 13 C α C 5 H 10 OAr 13 C α' C 5 H 10 OAr 13 C β C 5 H 10 OAr 13 C β' C 5 H 10 OAr 13 C γ C 5 H 10 OAr 13 C γ' C 5 H 10 O Ia Ib Ic P aa P bb P cc Planar Moments

Getting 17 O Chi gg values 16

17 MACHINE EXTERIOR

18 CAVITY INTERIOR Photo from Stew Novick

19 TIMING OF MB PROPAGATION Nozzle injects MB into cavity parallel to MW pulse propagation MW pulse with high Q polarizes sample, polarization decay measured, FT of data taken, doublet seen

20 FID Resonance frequency from molecule if present, within a 1 MHz width Fourier-Transform of free-induction decay of polarization of the radiation emitted by the molecules FT takes time resolved data to generate frequency domain data

21 FT of FID Results

22 QUADRUPOLE SPLITTING Arises from nuclear spin greater than 1/2 17 O has nuclear spin +5/2 F=I+J, where F is tot. ang. mom., J is ang mom. w/o nuclear spin, I splits the rot. transitions primarily from p orbital, measures electric field gradient at nucleus Kang, L., Minei, A., Novick, S., et al. J. Chem. Phys Namiki, Kei-ichi. et al. J. Mol. Spec

23 F level splitting