Chirped pulse rotational spectroscopy 71st International Symposium on Molecular Spectroscopy WC01 Chirped pulse rotational spectroscopy of a single thujone+water sample Zbigniew Kisiel, Institute of Physics, Polish Academy of Sciences, Warszawa, Poland Cristobal Perez, Melanie Schnell, CoCoMol, Max-Planck-Institut fur Struktur und Dynamik der Materie, Hamburg, Germany

Early investigation using Low-resolution Microwave Spectroscopy (LRMW): Under suitable conditions rotational spectrum collapses to a series of equally spaced lines with spacing equal to B+C Thujone: B+C =1522.1(5) MHz   = 15o Isothujone: B+C =1416.8(18) MHz   = 25o Kisiel + Legon, JACS 100, 8166 (1978) assumptions based on 3-bicyclo[3.1.0]hexanone, Bevan et al. JACS 100, 8161 (1978)

Chirped pulse spectrum recorded in Hamburg: Praha2008 Chirped pulse spectrum recorded in Hamburg: -Thujone Commercial thujone sample: 70% -thujone 10% -thujone (isothujone) 20% unspecified…. Conditions similar to those used in the recent camphor+water study: J.Phys.Chem.Lett. 7, 154 (2016): He carrier gas, 3.5bar, passed over 1:1 H216O:H218O, then over thujone gas pulses @ 4Hz, 8 chirps per gas pulse 1.4M FIDs averaged = 12 hr Aim: study the natural product monomers + their hydration clusters -Thujone = Isothujone

Visibility of 13C thujone in natural abundance: Praha2008 Visibility of 13C thujone in natural abundance: Parent species, 403 ← 302 (Kaiser-Bessel windowing function mandatory) J = 7 ← 6, Ka = 1 ↔ 0 a- + b-type quartet for thujone-(H2O)2 13C1 13C5 13C3 13C2

Visibility of 18O thujone in natural abundance: Praha2008 thujone+H218O: 532 ← 431 13C6 thujone: 403 ← 302 18O thujone: 413 ← 312

Praha2008 Assigned species: Assignment and analysis carried out using various combinations of AUTOFIT, AABS, JB95, SPFIT/SPCAT and quantum chemistry calculations -Thujone: parent (23 aR-, 13 bR-, 56 bQ-, 7 cR-, 11 cQ-type transitions) + all ten single 13C species + 18O species -Thujone = Isothujone: parent (also a-, b-, and c-type transitions) Thujone-II: similar to -Thujone but differing in isopropyl orientation, parent species Fenchone: parent (also a-, b-, and c-type transitions) + all ten single 13C species -Thujone + H2O: two isomers and their H218O isotopologues -Thujone + 2H2O: parent + single and double H218O isotopologues

Rotational constants old and new: Praha2008 ------------------------------------------------------------------------- THUJONE ISOTHUJONE this work 1978 this work 1978 A /MHz 1791.36164(46) 2034.06293(50) B /MHz 786.92929(31) 738.53792(26) C /MHz 739.71325(31) 677.08645(25) B+C /MHz 1526.64254(44) 1522.1(5) 1415.62437(36) 1416.8(18) DJ /kHz 0.0429(63) 0.0119(37) DJK /kHz 0.0056(42) 0.0514(65) DK /kHz 0.106(22) 0.0 dJ /kHz 0.00939(23) 0.00302(54) dK /kHz 0.205(14) -0.532(35) Nlines 108 75 sigma/kHz 5.94 5.34

Unfortunately thujone has multiple small atomic coordinates: Praha2008 The r0 structural fit (26 parameters to 36 rotational constants) is very satisfactory but precision is degraded to: 0.009 – 0.020 Å for r(CC) 0.5 – 1.1° for  (CCC)

 Thujone skeletal angles old and new:  1978: 15 expt. 18.4(19) Praha2008  1978: 15 expt. 18.4(19) calc. 19.6  1978: 66.9 expt. 70.3(12) calc. 70.8  ISOTHUJONE: 1978 25 Calc 21.4 expt. 62.7(22) calc. 61.6 expt. 85.3(21) calc. 88.9 expt. 125.5(22) calc. 125.1

Fenchone (+ its 13C species) and another thujone isomer: Praha2008 Fenchone (+ its 13C species) and another thujone isomer: expt. calc. A /MHz 1944.87920(54) 1940.87 B /MHz 774.61966(25) 778.49 C /MHz 667.56270(25) 673.39 Thujone-II Fenchone expt. calc. A /MHz 1555.75239(28) 1558.5 B /MHz 1168.26609(32) 1172.2 C /MHz 961.42050(32) 964.5 Assignment of fenchone was attempted since it is stated to be a significant constituent of most thuja oils. Fenchone is similar to camphor, and camphor lines have also been seen. STOP PRESS! Donatella Loru + Maria Sanz from King’s College London have also studied fenchone – see talk WC11

Thujone + single water molecule clusters: Praha2008 Calculated to be the more stable conformer. This is similar to the situation for camphor-water. a , b , and c allowed transitions observed

Thujone + 2 water molecules cluster: Praha2008 Thujone + 2 water molecules cluster: Structure determined from fit to 12 rotational constants for four isotopic species: parent, two single H218O, one double H218O ± 0.007 Å ± 0.006 Å

SUMMARY: A single chirped pulse spectrum recorded in 12 h allowed: Praha2008 SUMMARY: A single chirped pulse spectrum recorded in 12 h allowed: Assignment of rotational spectra and determination of spectroscopic constants for 4 different natural product molecules Determination of heavy atom backbones of 2 molecules from isotopic species in natural abundance Assignment of 3 different hydration clusters and parameters of their intermolecular bonds from H218O substitution Thujone is a natural product with an intriguing connection to human culture: Thujone  Absinthe  Piołunówka …mysterious, addictive, and mind- altering drink…. L’Absinthe, by Edgar Degas, 1876 (Wikipedia)