Millimeter-wave spectroscopy of formyl azide (HC(O)N3) Nicholas A. Walters, Brent K. Amberger, Brian J. Esselman, R. Claude Woods, Robert J. McMahon University of Wisconsin June 26, 2015

Formyl azide (HC(O)N3) No rotational data in the chemical literature Spectroscopic findings include IR, UV and NMR spectra, as well as crystallographic data1,2 Structurally similar to HN3 and C(O)(N3)2 Banert and Hagedorn are common to each paper Solution phase studies via IR, UV and NMR spectroscopies in CCl4 – ref 1 from tbo Interesting to us because it shares structural similarities to molecules like HN3 and carbonyl diazide, both of which have been studied by our group. According to calculations at CCSD(T) level of theory with ANO1 basis set, the two isomeric forms of formyl azide (syn or anti configuration of the C=O and N3 groups with respect to the C-Na bond) which we expect to see in the gas phase differ in energy by 2.8 kcal/mol Cs symmetry Syn-isomer Anti-isomer Relative E (kcal/mol) (CCSD(T)/ANO1) 2.8 1. Banert, K. et al. Angew. Chem. Int. Ed. 2012, 51, 4718-4721 2. Zeng, X. et al. Angew. Chem. Int. Ed. 2013, 52, 3503-3506

Synthesis Highly unstable molecule at room temperature t1/2~ 20 min in CDCl3 t1/2~ 2 hours in gas-phase Sample frozen in liquid nitrogen Outlines the simplest version of a Curtius rearrangement LN2 trap to crudely remove water, ethylene glycol and dry ice to remove more water and allow formyl azide through Dry ice-ethylene glycol trap used to remove water from sample – allowed FA through, while other traps didn’t? Banert, K. et al. Angew. Chem. Int. Ed. 2012, 51, 4718-4721

Spectrum collection ~10 mTorr 250-360 GHz Room temperature Mention about 8 hours per segment of about 20-25 GHz Sample through series of traps before reaching sample chamber to Sample pressure not super precise as we bleed in gas evolved from the sample initially containing water vapor as well Mention how some spectral range segments aren’t as strong as others due to sample either being “tired” toward the end of data collection or the sample decaying more rapidly in some segments We put up to 20 mTorr of sample into our sample chamber of 3 m in length. We then sweep the frequency of the source (250-360 GHz) while detecting the intensity of transmitted radiation, resulting in our absorption spectrum which we can use to analyze our molecule.

Syn-isomer predicted spectra μa (D) μb (D) μc (D) 0.224 1.547 Syn-isomer ground state Ground states Note how b-type transitions dominate in syn, a-type transitions dominate in anti CCSD(T)/ANO1

Syn-isomer spectral characteristics b-type Q-branch transitions Experiment k-1 1413 transitions Ground state fit Kprolate 14<-13 series of ground state First line in series is J 14, note the turnaround around J 16 Showing the anatomy of the spectral features while showing the good agreement of the fit with experiment J=19 J=18 J=17 J=16 J=14 J=15

Syn-isomer spectral characteristics - continued b-type R-branch transitions Experiment k-1 10 transitions Ground state fit Kprolate 10 transitions Point out kprolate 10, 21, 32 and 43 transitions and note the general progression seen within a clump of R-branch transitions. Can take a closer look at these transitions to see a repeating “clump” of transitions k-1 21 k-1 32 k-1 34 k-1 43 k-1 45 k-1 54 k-1 10

Fit of syn-isomer ground state CCSD(T)/ANO1 Experimental constants A (MHz) 15841.18705587 B (MHz) 4264.02895199 C (MHz) 3354.64756031 ΔJ (kHz) 4.33087 ΔJK (kHz) -37.5978 ΔK (kHz) 142.249 δJ (kHz) 1.36587 δK (kHz) 8.34156 A (MHz) 15992.41390(92) B (MHz) 4299.03654(28) C (MHz) 3383.17621(28) ΔJ (kHz) 4.46190(16) ΔJK (kHz) -38.67389(48) ΔK (kHz) 148.8241(65) δJ (kHz) 1.412399(28) δK (kHz) 9.22476(98) ΦJ (Hz) 0.016036(32) ΦJK (Hz) -0.01143(21) ΦKJ (Hz) -1.0602(17) ΦK (Hz) 4.448(13) φJ (Hz) 0.0077153(74) φJK (Hz) 0.02631(28) φK (Hz) 1.9886(38) LJJK (mHz) 0.000390(12) LJK (mHz) -0.01061(25) LKKJ (mHz) 0.0739(12) lJ (mHz) -0.00003660(50) n 1236 Again, mention types of transitions included in fit May just take the time to mention low-intensity a-type R-branch transitions which are included in fit as well (only a handful of these included in fits – not used in higher energy vibrationally excited states). Constants came from fak3ab.asf – could include more distortion terms to decrease fit deviation, however adding in more marginally changes the deviation

Syn-isomer excited vibrational states 670.86 cm-1 2ν12 + ν9 590.04 cm-1 2ν9 + ν12 582.60 cm-1 ν11 509.22 cm-1 3ν9 501.12 cm-1 2ν12 489.40 cm-1 ν8 420.30 cm-1 ν9 + ν12 Now began to assign transitions belonging to higher energy vibrationally excited states 339.48 cm-1 2ν9 250.56 cm-1 ν12 169.74 cm-1 ν9 0 cm-1 ground

Syn-isomer: ν9 (169.74 cm-1) Loomis Wood plot based on calculations for ν9 (centered on bQ k-1 1413 series) A (MHz) 16046.9479(13) B (MHz) 4305.49157(43) C (MHz) 3382.56031(51) ΔJ (kHz) 4.47120(26) ΔJK (kHz) -39.04914(57) ΔK (kHz) 153.241(10) δJ (kHz) 1.422331(31) δK (kHz) 10.0188(21) ΦJ (Hz) 0.015746(47) ΦJK (Hz) -0.00421(59) ΦKJ (Hz) -1.1422(22) ΦK (Hz) 4.968(23) φJ (Hz) 0.0073927(85) φJK (Hz) 0.02878(65) φK (Hz) 2.2411(94) n 955 Level of theory for calculation of alpha values should be put in somewhere – CCSD(T)/ANO1, same as previous calculations LW plot centered on b-type Q-branch series of kprolate 1413 – shows how useful initial predictions from computations were in finding vibrational states of the syn isomer, as this LW plot was generated just from computed rotation-vibration interaction terms A’ (totally symmetric) Calculation Experiment αA -55.065 -54.538 αB -6.540 -6.455 αC 0.605 0.617

Syn-isomer: ν12 (250.56 cm-1) Loomis Wood plot based on calculations for ν12 (centered on bQ k-1 1211 series) A (MHz) 16044.6287(17) B (MHz) 4288.83396(65) C (MHz) 3382.39139(77) ΔJ (kHz) 4.44996(40) ΔJK (kHz) -39.07071(83) ΔK (kHz) 150.685(14) δJ (kHz) 1.403817(49) δK (kHz) 9.3096(42) ΦJ (Hz) 0.015582(74) ΦJK (Hz) 0.0041(12) ΦKJ (Hz) -1.1317(39) ΦK (Hz) 4.662(30) φJ (Hz) 0.007256(14) φJK (Hz) 0.0286(12) φK (Hz) 2.2411(94) n 785 Another example of the same Q-branch series predicted well again for v12. A’’ (anti-symmetric) Calculation Experiment αA -49.079 -52.219 αB 9.867 10.203 αC 0.717 0.786

Syn-isomer: 2ν9 (339.48 cm-1) Loomis Wood plot based on calculations for ν12 (centered on bR k-1 21 series) A (MHz) 16102.1822(17) B (MHz) 4312.18472(60) C (MHz) 3382.11340(71) ΔJ (kHz) 4.49157(35) ΔJK (kHz) -39.43803(90) ΔK (kHz) 157.603(14) δJ (kHz) 1.435835(57) δK (kHz) 10.8323(51) ΦJ (Hz) 0.016523(62) ΦJK (Hz) 0.0140(15) ΦKJ (Hz) -1.2525(51) ΦK (Hz) 5.207(31) φJ (Hz) 0.007701(14) φJK (Hz) 0.0233(15) φK (Hz) 2.657(29) n 757 Mention how series to the left are lower-energy vibrational states’ R-branch transitions – likely ground and v9 or v12 A’ (totally symmetric) Calculation Experiment αA -110.130 -109.772 αB -13.080 -13.148 αC 1.210 1.064

Syn-isomer: ν9 + ν12 (420.30 cm-1) Syn-isomer: ν11 (582.60 cm-1) A (MHz) 16098.4725(16) B (MHz) 4294.65062(61) C (MHz) 3381.62697(70) ΔJ (kHz) 4.45740(36) ΔJK (kHz) -39.39287(91) ΔK (kHz) 155.296(14) δJ (kHz) 1.413383(62) δK (kHz) 10.0407(51) ΦJ (Hz) 0.015795(66) ΦJK (Hz) 0.0088(15) ΦKJ (Hz) -1.1998(52) ΦK (Hz) 5.021(30) φJ (Hz) 0.007367(16) φJK (Hz) 0.0233(15) φK (Hz) 2.657(29) n 672 A (MHz) 16082.2278(68) B (MHz) 4296.0936(26) C (MHz) 3382.4443(30) ΔJ (kHz) 4.4781(15) ΔJK (kHz) -39.1152(51) ΔK (kHz) 157.442(57) δJ (kHz) 1.41488(32) δK (kHz) 9.696(31) ΦJ (Hz) 0.01743(30) ΦJK (Hz) 0.0281(81) ΦKJ (Hz) -1.197(30) ΦK (Hz) 4.97(12) φJ (Hz) 0.007703(84) φJK (Hz) φK (Hz) 2.77(15) n 493 Fit deviation increases marginally with more distortion terms, however the distortion term values themselves have larger errors associated with them Using favib7and8b.v11 is A’’ (anti-symmetric) Calculation Experiment αA -104.144 -106.059 αB 3.327 4.386 αC 1.322 1.549 Calculation Experiment αA -85.445 -89.814 αB 2.704 2.943 αC 0.772 0.732

Excited vibrational states of the syn-isomer 670.86 cm-1 2ν12 + ν9 590.04 cm-1 2ν9 + ν12 582.60 cm-1 ν11 509.22 cm-1 3ν9 Potential for Fermi resonance 501.12 cm-1 2ν12 489.40 cm-1 ν8 420.30 cm-1 ν9 + ν12 Looking at all of these vibrational states in the hopes of greatly simplifying search for anti-isomer by removing transitions from the experimental spectrum Summary of current fits obtained for vibrationally excited states Talk about 3v9, 2v12, v8 and potential perturbations between these states V9 is A’ (totally symmetric), so 3v9 is totally symmetric (A’) V8 is totally symmetric (A’) V12 is A’’ (anti-symmetric), so 2v12 is A’ (totally symmetric) Think Cs point group A’ 1 1 A’’ 1 -1 339.48 cm-1 2ν9 250.56 cm-1 ν12 169.74 cm-1 ν9 0 cm-1 ground

Anti-isomer predicted spectra Syn-isomer μa (D) μb (D) μc (D) 2.067 1.502 μa (D) μb (D) μc (D) 0.224 1.547 Anti-isomer Syn-isomer Relative E (kcal/mol) 2.8 Anti-isomer ground state Ground state Mention how transition spacing is different here than in the syn-isomer spectra, so finding the transitions using LW plots should be a bit easier Note how b-type transitions dominate in syn, a-type transitions dominate in anti Mention size of dipole moment being larger here than in syn, yet still much lower intensity due to higher energy conformation CCSD(T)/ANO1

Likely series associated with anti-isomer Loomis Wood plot (centered on aR k-1 11 series) This series is situated ~1267 MHz away from the initial prediction for the ground state of the anti-isomer based solely on constants from initial calculations Here, decided to show LW plot with triangles rather than full spectrum since these low-intensity lines are difficult to see in the full spectrum. You’ll notice these transitions are clear, up until about 320 GHz, at which point the transitions drop-off in intensity at a region of the spectrum in which the sample was a bit tired (one of the last sample chamber fills).

Summary and future work Fits obtained for several syn-isomer vibrational states: In progress: Investigate remaining syn-isomer vibrational states Examine potential perturbations between them Examine the inertial defect of 2ν9 + ν12 in an effort to find b-type R-branch transitions and obtain a fit Continue searching for/assigning anti-isomer ground state transitions Mention possible states perturbing one another and how you currently have fits for some transitions, just not well converged yet Need to examine inertial defect for 2v9+v12 because fit currently only includes bQ-branch transitions. Examining the inertial defect will give the rotational constants corresponding to the state Fits completed using the A-reduced Hamiltonian

Thanks! Prof. Robert J. McMahon Prof. R. Claude Woods Research Group: Dr. Brian J. Esselman Brent Amberger Ben Haenni Zachary Heim Matisha Kirkconnell Stephanie Knezz Vanessa Orr Cara Schwarz Maria Zdanovskaia