ABSOLUTE 17 O NMR SCALE: a JOINT ROTATIONAL SPECTROSCOPY and QUANTUM-CHEMISTRY STUDY Cristina PUZZARINI and Gabriele CAZZOLI Dipartimento di Chimica “G. Ciamician”, Università di Bologna Michael E. HARDING and Jürgen GAUSS Institut für Physikalische Chemie, University of Mainz Columbus — June 26, 2009
1) Experiment: Instrument & Technique Instrument & Technique
FREQUENCY RANGE LMSB (2) GHz (from fundamental to the 6th harmonic) GHz (8th harmonic) GHz (8th harmonic) (3) THz (9th harmonic) THz (12th harmonic) THz (12th harmonic) (1) GHz (wave-guide Stark cell – P band)
MILLIMETER-WAVE EXPERIMENTAL SET-UP (2) BLOCK DIAGRAM OF THE GHz SPECTROMETER SYNTH 10 kHz-1 GHz MULT fSfS nfSnfS MIX MULT SYNCR ref: 20 MHz RF OSCILL GHz f RF 20 MHz 90 MHz |f G - mf RF | GUNN P. SUPPLY and SYNCR ref: 73 MHz |f RF - nf S | HP8642A SYNTH MIX corr fGfG fGfG MULTIPLIER InSb DETECTOR PREAMPL LOCK - IN 10 MHz freq. standard kHz ref GUNN DIODES THERMOSTAT or liquid N 2 system
Measurements: Lamb-dip technique Corner cube mirror Cell InSb detector Polarizer Frequency modulated source Scheme of the radiation path Using free-space cell G. Cazzoli & L. Dore, J. Mol. Spectrosc. 143, 231 (1990).
1) Partial saturation 2) Only Doppler profile 3) Rad: back and forward Measurements: Lamb-dip technique + v za - v za vz= 0vz= 0vz= 0vz= 0
( ) Lamb-dip effect
Measurements: Lamb-dip technique CH 2 BrF Doppler Lamb-dip the Lamb-dip technique allows 1) To well resolve hfs ( / = 3.9x10 7, =16 kHz) 2) To accurately determine - frequencies - frequencies - hfs parameters - hfs parameters
GHOST TRANSITIONS
2) Theory: Computational details & Computational details & requirements requirements
Parameters of Rotational Spectroscopy Effective Hamiltonian: determination of H Rot via quantum chemistry Rotational Hamiltonian Rotational constants Nuclear quadrupole coupling constants Spin-rotation interactions Spin-spin (direct) interactions interactions
Quantum-Chemical Calculation of Spectroscopic Parameters Nuclear quadrupole coupling Nuclear quadrupole coupling first-order property: requires first derivatives of energy Spin-rotation interaction Spin-rotation interaction second-order property: requires second derivatives of energy ELECTRIC FIELD GRADIENT
requires equilibrium geometry: no „electronic property“ addditional contribution due to: indirect spin-spin coupling (usually negligible) Quantum-Chemical Calculation of Spectroscopic Parameters Spin-spin coupling Spin-spin coupling DIPOLAR SPIN-SPIN COUPLING TENSOR vibrational corrections (anharmonic force field)
Beyond the Rigid-Rotator Approximation COUPLING of ROTATIONAL and VIBRATIONAL MOTION Vibrational corrections to properties: PERTURBATION THEORY starting from the rigid-rotator harmonic oscillator approximation the rigid-rotator harmonic oscillator approximation Vibrational corrections require: anharmonic force field calculations anharmonic force field calculations
Accurate hyperfine parameters >>>> Main requirements : - accurate method - cc basis set - CV corrections
Accurate hyperfine parameters >>>> Main requirements : - accurate method [CCSD(T)] - cc basis set [n Q] - CV corrections [additivity/CV bases]
Accurate hyperfine parameters >>>> Main requirements : - accurate method [CCSD(T)] - cc basis set [n Q] - CV corrections [additivity/CV bases] - vibrational corrections
Accurate hyperfine parameters >>>> Main requirements : - accurate method [CCSD(T)] - cc basis set [n Q] - CV corrections [additivity/CV bases] - vibrational corrections [ff: -correlated method method -basis: n T] -basis: n T]
3) Results 3) Results
Lamb-dip spectra recorded Hyperfine parameters computed Spectra analysis & assignment
Para lines Para lines (I H,tot = 0) hfs: only 17 O
Hyperfine parameters ………. 17 O: -nuclear quadrupole coupling -spin-rotation H: H: —
Ortho lines Ortho lines (I H,tot = 1) hfs: 17 O + H
Hyperfine parameters ………. 17 O: -nuclear quadrupole coupling -spin-rotation -spin-spin ( 17 O-H) H: H: -spin-rotation -spin-spin (H-H)
J = 1 1,0 – 1 0,1
17 O ExperimentTheory C aa (11) C bb (81) C cc (54) Results ……. results in kHz
Method:CCSD(T)Equil. (exp r e ) Vib. Corr. (VPT2) (DVR)Total(Eq+Vib) basis basisaugCV6ZaugCV5ZaugCV5Z C aa C aa C bb C bb C cc C cc
„Experimental“ Determination of Absolute Shieldings measure rotational spectrum extract nuclear spin-rotation constant subtract rovibrational corrections convert to paramagnetic shielding add calculated diamagnetic shielding add rovibrational corrections consider temperature effects experiment C v,J C e σ e para σ e dia σ v,J σ(T)
Results …… Absolute 17 O NMR scale [ppm] [ppm]isotropic (dia) calculated (para) from exp (equil) (vib) (T) (3) (300K) 326.2(3) Best theoretical estimate ppm
Results …… the other hf parameters [MHz/kHz] [MHz/kHz]ExperimentTheory 1.5 aa ( 17 O) (25) MHz MHz ( bb - cc )/4 ( 17 O) (52) MHz MHz 1.5D aa ( 17 O-H) 23.44(43) kHz kHz (D bb -D cc )/4 ( 17 O-H) 5.182(97) 5.11 kHz 5.11 kHz 1.5D aa (H-H) (25) kHz C aa (H) (30) kHz kHz C bb (H) (25) kHz kHz C cc (H) (12) kHz kHz
Calculations performed using C FOUR : THANK YOU for your attention!! THANK YOU for your attention!!
NMRMW Bryce & Wasylishen, Acc. Chem. Res. 36, 327 (2003) connection nuclear magnetic shielding absolute shielding scales Ramsey-Flygareequations form of Hamiltonians: coupling mechanism vs tensor rank nuclear quadrupole coupling nuclear quadrupole coupling C Q nuclearspin-rotationCchemicalshift tensor spin-spin coupling (rank 2) C 3 scalar spin-spin coupling (rank 0) C 4 direct dipolar couplingD indirect spin-spin couplingJ
Frerking, Langer, J. Chem. Phys. 74, 6990 (1981) Radioastronomical study (Bok globule B335) Absolute 17 O NMR Scale OLD
C( 17 O)-30.4(12) C(vib) -0.1 (para) (172) (dia) (eq) -38.7(172) (vib) (T) (300K) -44.8(172) Wasylishen et al., JCP 84, 1057 (1984); Sundholm, Gauss, Schäfer JCP 105, (1996) Best theoretical estimate ppm OLD
Cazzoli, Dore, Puzzarini, Beninati, Phys. Chem. Chem. Phys. 4, 3575 (2002) New laboratory study using Lamb-dip technique Absolute 17 O NMR Scale NEW
C( 17 O)-30.4(12)-31.61(4) C(vib) -0.1 (para) (172)-501.8(6) (dia) (eq) -38.7(172)-56.7(6) (vib) (T) (300K) -44.8(172)-62.7(6) Wasylishen et al., JCP 84, 1057 (1984); Sundholm, Gauss, Schäfer JCP 105, (1996) Best theoretical estimate ppm OLDNEW