61 st OSU International Symposiumon Molecular Spectroscopy RI

61 st OSU International Symposiumon Molecular Spectroscopy RI 14 Assignment of. GG , GG ’, TT , and TG conformers in the. FASSST rotational spectrum ofn-propanol Zbigniew Kisiel, Orest Dorosh Institute of Physics, Polish Academy of Sciences Atsuko Maeda, Frank C. De Lucia, Eric Herbst Department of Physics, The Ohio State University

TT TG (two identical) Rotation of CH 2 OH about CC GT Rotation of OH about CO GG GG’

Most relevant previous studies: Abdurakhmanovet al. : several papers over the period 1967 -1987, cm-wave rotational studies of n-propanol. gauche form estimated to be the most stable one. Dreizler & Scappini, Z. Naturforsch. 36 a, 1187 (1981): b- type cm-wave rotational spectrum of the TT species Maeda et al. , Astrophys. J. Suppl. Ser. 162, 428 (2006): over 2400 lines of the GT conformer up to 375 GHz assigned and fitted Kahn & Bruice, Chem. Phys. Chem. 6, 487 (2005): detailed ab initio analysis of relative energies. In the preferred result GT is the global minimum with GG, GG’ at 38, 52 cm-1 resp. , TT, TG are at 28, 45 cm-1 resp.

Ab initio* spectroscopic observables forn-propanol: A B C /MHz DJ /k. Hz DJK DK d. J d. K GT GG 14339 5102 4307 14100 5019 4280 GG’ 14216 5034 4227 TT 26579 3784 3531 TG 26147 3734 3508 5. 40 -23. 8 64. 1 1. 59 11. 9 5. 09 -21. 7 58. 4 1. 43 10. 1 5. 54 -25. 9 69. 6 1. 65 11. 2 m_a /D m_b m_c 0. 71 0. 87 0. 96 0. 56 1. 04 1. 09 1. 39 0. 12 0. 87 0. 09 1. 46 0 1. 15 0. 39 1. 15 m_tot 1. 48 1. 61 1. 65 1. 46 1. 68 * Unscaled B 3 LYP/6 -31 G(d, p) 0. 828 -2. 35 58. 7 0. 0737 0. 361 0. 840 -2. 61 57. 6 0. 0737 1. 10

Satellite line sequence (GT excited state) Ka = 1 - 0 of GT

Confirmation of the assignment of the. GT conformer GT gs A B C /MHz DJ /k. Hz DJK DK d. J d. K N s /k. Hz 14330. 37308(45) 5119. 30843(16) 4324. 20213(16) 5. 66401(22) -24. 6960(11) 67. 8861(38) 1. 687806(53) 12. 56606(88) 2861 63. 1 * Unscaled B 3 LYP/6 -31 G(d, p) =1 14378. 5960(21) 5104. 59867(93) 4318. 31841(57) 5. 74650(85) -26. 4520(35) 75. 088(12) 1. 71737(36) 13. 027(14) 308 83. 1 ab initio* 14339 5102 4307 5. 40 -23. 8 64. 1 1. 59 11. 9

Cavity-FTMW Stark measurements for. GT n-propanol

Dipole moments for. GT and TT n-propanol DFT and MP 2 with 6 -31 G(d, p) give ma 0. 1 D

Bands in the FASSST spectrum: Band system A @ 9. 35 GHz Band system B @ 7. 2 GHz Band system C @ 19. 15 GHz MHz Typical band spacing: B + C for R-type bands 2 A – (B + C) for Q-type bands

Band A: J = 17 16 of GG’

Band C: Ka = 9 8 c. Q+b. Q of GG (white left), GG’ (white right), GT (yellow right)

Distribution of mixing coefficients and data points: 1 – Pmix obs-calc GG GG’

Comparison of spectroscopic constants: GT A B C /MHz DJ /k. Hz DJK DK d. J d. K GG 14330. 37308(45) 5119. 30843(16) 4324. 20213(16) 5. 66401(22) -24. 6960(11) 67. 8861(38) 1. 687806(53) 12. 56606(88) DE/MHz N s /k. Hz ab initio A B C /MHz GG’ 14206. 741(25) 14258. 160(25) 5036. 7229(41) 5050. 7618(39) 4290. 3029(27) 4253. 6136(25) 5. 36149(75) -23. 261(12) 63. 384(57) 1. 51462(33) 11. 244(20) 5. 22356(91) -24. 019(28) 68. 923(62) 1. 54892(39) 11. 604(18) 90988. 67(11) 2861 63. 1 E(GG’) B 3 LYP/6 -31 G(d, p) 14339 5102 4307 3114 - E(GG) = 3. 035103. 9 055(4) cm-1 E(GG) - ab initio 14 cm-1 14100 14216 * -1 E(GT) 5019 *40 cm ? 5034 4280 (three * 4227 state fit required)

Effective fit for. TT : TT A B C ab initio /MHz 26401. 5164(50) 3802. 15219(57) 3549. 46158(60) DJ /k. Hz DJK DK d. J d. K 0. 99790(43) 0. 302(62) 153. 9(17) 0. 12508(46) -9. 20(18) N s 232 0. 11 but only to Ka=0. . 2 /MHz 26579 3784 3531 0. 828 -2. 35 58. 7 0. 0737 0. 361 ! The torsional potential section giving rise to TT, TG +, TG - states is analogous to that for ethanol that results in T, G+, G- states. But for ethanol E(G+) - E(T) 40 cm-1 and a single state fit is possible for a broad range of T-state transitions.

Band B: J = 31 30 of TG +

Ka = 9, a. R-type transitions for TG + Analogous a. R-type bands for TG -

Ka = 0, a. R-type transitions for TG + Ka = 0, a. R-type transitions for TG -

Preliminary coupled fit for. TT TG + : TT A B C /MHz DJ /k. Hz DJK DK d. J d. K TG + 26422. 79(91) 3802. 3984(63) 3549. 4244(18) 1. 0052(14) [-2. 4] [58. 7] 0. 12428(77) [ 0. 36] DE/MHz 0. 9050(50) [-2. 606] [57. 6] 0. 0974(54) [ 1. 096] 352043. (884) N 740 ab initio A B C 25524. 7(82) 3769. 085(49) 3535. 270(19) /MHz B 3 LYP/6 -31 G(d, p) 26579 3784 * 3531 E(TG +) - E(TT) = 11. 44(3) cm-1 26147 * 3734 3508 ab initio 17 cm-1

Principal conclusions: TT, TG, GT, GG ’ conformers have been assigned with confidence in the FASSST spectrum and all major bands are accounted for GG+GG ’ conformers are satisfactorily fitted in a coupled fit resulting in DE(GG’- GG) = 3. 035 055(4) cm-1 TT conformer is perturbed beyond Ka=1, TG conformer is perturbed even from Ka=0, for both TG + and TG - substates. TT , TG + and TG – are more mutually perturbed and are thus closer to each other than T, G+ and G– in ethanol ! Three state fits are still required: GT GG GG ’ would yield DE(GG- GT) TT TG + TG - is needed even for satisfactory description of the spectrum, and of course for DE’s