COMBINATION BANDS OF THE NONPOLAR N 2 O DIMER AND INFRARED SPECTRA OF (C 2 D 4 ) 2 AND (C 2 D 4 ) 3 USING A QUANTUM CASCADE LASER Mojtaba Rezaei, N. Moazzen-Ahmadi Department of Physics and Astronomy University of Calgary A.R.W. McKellar Steacie Institute for Molecular Sciences National Research Council of Canada K. H. Michaelian Natural Resources Canada, CANMET Western Research Center

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Jet Trigger 12 bit DAQ Card Timer Controller Card (CTR05) DAQ Trigger Gas Supply Ref. Gas Jet Signal IR Detectors Etalon QCL PZT Controller Function Generator Valve Controller (Iota One)

Current ramp to TDL from L5830 Trigger from L5830 DAQ Card records 4000 points 4MHz Jet trigger to Iota One from CTR05 Actual jet opening (approx.) d1 d2 Background Dummy Jet signal Time sequence for data acquisition (TDL) 1 kHz ~ 2.5 ms 1 ms

Time sequence for data acquisition (QCL)

reference gas signal boxcar gates Reference gas cell Sweep stabilization using 2-channel boxcar 2-channel boxcar integrator SR250 ab PZT controller output(b  a) oscilloscope De Piante, Campbell, & Buelow, Rev. Sci. Instr. 60, 858 (1989) TTL  Function generator

Linewidth: Laser Locked: 500 averages Linewidth:Free running: 50 averages Enhanced resolution! Sweep stabilization using 2-channel boxcar

Background Averaged spectrum Jet signal Background subtracted Ref. Gas signal Etalon LabView Snapshot of the computer screen during data acquisition

Comparison between recorded spectra with TDL and QCL Recorded with QCL* averages Recorded with TDL** averages Comparison of spectra for ( 14 N 2 O) 2 torsional combination band using Tunable Diode Laser (TDL) and Quantum Cascade Laser (QCL) * M. Rezaei, K. H. Michaelian, and N. Moazzen-Ahmadi, J. Chem. Phys. 136, (2012) ** M. Dehghany, M. Afshari, Z. Abusara, and N. Moazzen-Ahmadi, Phys. Chem. Chem. Phys. 11, 7585 (2009).

4D (including only the intermolecular modes) PES Global minimum: nonpolar-O-in structure in good agreement with experiment. Higher energy structure: Polar, also in good agreements with experiment Plus two T-shaped higher energy isomers (neither of which have been observed). Binding energy (cm -1 )  633  465

Intermolecular modeCCSD(T)F12b/VTZ-F12 a CCSD(T) Aug-cc-pVDZ b Out-of-plane torsion (A u ) Geared bend (B u ) Antigeared bend (A g ) van der Waals stretch (A g ) Calculater intermolecular vibrational frequencies for the nonpolar (N 2 O) 2 (in cm -1 ) a R. Dawes, X.-G. Wang, A. W. Jasper, and T. Carrington, Jr., J. Chem. Phys. 133, (2010). b L. Zheng, Y. Lu, S.-Y. Lee, H. Fu, and M. Yang, J. Chem. Phys. 134, (2011).

Intra- Molecular In-phase combination of the two N 2 O monomers 1 stretches A g (infrared inactive) Out-of-phase combination of the two N 2 O monomers 1 stretches B u (infrared active) Inter- molecular AuAu BuBu AgAg AgAg AuAu BuBu AgAg AgAg CombinationAuAu BuBu AgAg AgAg BgBg AgAg BuBu BuBu Infrared Activity  Band type ca,b Symmetry and band type for combination bands of nonpolar N 2 O dimer in the 1 region (2220 cm -1 ) of the monomer

Determination of frequency for the infrared forbidden intramolecular in-phase combination of the two N 2 O monomers 1 stretches: 1.Measure the bands centers for ( 14 N 2 O) 2, ( 15 N 2 O) 2, and 14 N 2 O- 15 N 2 O from infrared bands 2.Use the resonant dipole-dipole model Or Vibrational shifts from ab initio calculation. Berner et al., J. Chem. Phys. 130, (2009).

Experimental conditions Experimental system:- Pulsed slit Jet - Quantum Cascade Laser probe (rapid scan signal averaging mode) - Number of laser passes through the jet: >100 Mixture: A dilute mixture of N 2 O (0.3%) in He. Backing pressure: 7.5 Atmospheres Frequency Calibration:Reference gas: N 2 O Etalon FSR: cm -1

The torsional combination bands Rotational temperature of 2.5 K Linewidths : 0.003cm -1 The simulated spectra were made with PGOPHER averages With QCL

The antigeared combination bands Rotational temperature of 2.5 K Linewidth for ( 14 N 2 O) 2 : cm -1 (recorded with TDL) Linewidth for ( 15 N 2 O) 2 : cm -1 (recorded with QCL) averages With TDL averages With QCL

a M. Rezaei, K. H. Michaelian, and N. Moazzen-Ahmadi, J. Chem. Phys. 136, (2012) b M. Dehghany, M. Afshari, Z. Abusara, and N. Moazzen-Ahmadi, Phys. Chem. Chem. Phys. 11, 7585 (2009). Intermolecular mode( 14 N 2 O) 2 ( 15 N 2 O) 2 Out-of-plane torsion (A u ) 27.3(1.0) a 26.9(1.0) a Geared bend (B u ) 41.3(1.0) b 41.6(1.0) b Van der Waals stretch (A g ) Antigeared (A g ) (1) c (1) c Observed intermolecular vibration frequencies for nonpolar ( 14 N 2 O) 2 a nd ( 15 N 2 O) 2 (in cm -1 ) Intermolecular modeExp.CCSD(T)F12b/VTZ-F12CCSD(T) Aug-cc-pVDZ Out-of-plane torsion (A u ) 27.3(1.0) Geared bend (B u ) 41.3(1.0) Van der Waals stretch (A g ) Antigeared bend (A g ) (1) Comparison of observed and calculated intermolecular vibration frequencies for nonpolar ( 14 N 2 O) 2 (in cm -1 )

Previous works on ethylene clusters  M.A. Ho ff bauer, et al., Springer Ser. Chem. Phys., 1979, 6, 252.  M.P. Casassa, et al., J. Chem. Phys., 1981, 74,  A. Mitchell, et al., J. Chem. Phys., 1985, 83, 4271  M. Snels, et al., Chem. Phys. Lett., 1986, 124, 1.  K.G.H. Baldwin and R. O. Watts, Chem. Phys. Lett., 1986, 129, 237.  W.L. Liu, et al., Chem. Phys. Lett., 1984, 112, 585.  G. Fischer, et al., J. Chem. Phys., 1985, 83,  M. C. Chan, et al., J. Chem. Phys., 1995, 102,  R. Ahlrichs, et al., Z. Phys. D: At. Mol. Clusters, 1990, 15, 341.  H. Takeuchi, Comput. Theor. Chem., 2011, 970, 48.  Y.N. Kalugina, et al., J. Comput. Chem. 2012, 33, 319.

C 2 H 4 dimer Cross-shaped structure, D 2d symmetry M.C. Chan, P.A. Block, and R.E. Miller, JCP, 102, 3993 (1995). Both vibrational bands show homogeneous broadening corresponding to vibrational predissociation lifetimes of 0.37 and 0.18 ns for 9 and 11 excitation, respectively Red shift: cm Red shift: cm -1

Experimental conditions Experimental system:-Pulsed slit jet - Quantum Cascade Laser probe (rapid scan signal averaging mode) - Number of laser passes through the jet: >100 Mixture: A dilute mixture of C 2 D 4 (0.35%) in He. Backing pressure: 7.5 Atmospheres Probed region:the 11 fundamental band of C 2 D 4 (2200 cm -1 ) Frequency Calibration:Reference gas: N 2 O Etalon FSR: cm -1

Perpendicular band assigned to C 2 D 4 dimer Simulation program: PGOPHER. Rotational temperature: 3 K Linewidth of the Q-branches: cm -1 The sharpest lines have linewidth of cm -1 Upper state vibrational lifetime: 0.9 – 2ns Red shift of cm -1 with respect to C 2 D 4 monomer 11 band origin 11  excitation 

Molecular parameters for C 2 D 4 dimer ParameterGround stateExcited state 0 / cm (1) A / cm (104) (62) B / cm (18) (17) Intermolecular distance for C 2 H 4 dimer: (Chan et al.)

Parallel band assigned to C 2 D 4 trimer Simulation program: PGOPHER. Rotational temperature: 3 K Linewidth of the Q-branch: cm -1 Red shift of – cm -1 with respect to C 2 D 4 monomer 11 band origin

C 2 D 4 trimer with C 3h or C 3 symmetry Parallel trimer, C 3h Symmetry Twisted trimer, C 3 symmetry Tilt angle < 20  Top viewSide view

Molecular parameters for C 2 D 4 trimer ParameterGround stateExcited state 0 / cm (1) B / cm (67) (64) C / cm D J / cm -1 Parallel trimerTwisted trimer

 We have successfully implemented a QCL in the rapid scan signal averging mode.  We have measured three of the four intermolecular modes of the nonpolar N 2 O dimer. These are in very good agreement with theoretical calculations.  C 2 D 4 dimer and trimer have been observed in the region of the monomer 11 fundamental (~2200 cm -1 ).  The two bands observed indicate that: 1.The dimer has cross-shaped structure with D 2d symmetry 2. The trimer has a barrel-shaped structure with C 3h or C 3 symmetry.  Results for C 2 D 4 dimer support the previous works. Summary