1. The Pure Rotational Spectrum of TiCl + (X 3  r ) by Velocity Modulation Spectroscopy DeWayne T. Halfen and Lucy M. Ziurys Department of Chemistry Department of Astronomy Steward Observatory Arizona Radio Observatory University of Arizona June 21, 2004

2. Why Molecular Ions ? Chemical Aspect –Organic intermediates –Stratospheric chemistry –Combustion chemistry Astronomical Aspect –Many molecular ions in interstellar medium Radicals – Difficult to study –Few molecular ions studied at high resolution Ions Studied at High Resolution H3+H3+ CO + CH + SO + HCO + HOC + H2D+H2D+ HCS + N2H+N2H+ H3O+H3O+ CH 2 D + HCNH + HOCO + H 2 COH + HC 3 NH + OH + OH  HCl + ArH + HBr + Neutral species dominate over ions Built a new spectrometer – uses Velocity Modulation –Ion selective technique

3. Velocity Modulation Spectrometer

4. Detector Radiation Source Gas Cell Reactant

5. Characteristics of Velocity Modulation Drift velocity of TiCl + – –E = 1.9 V/cm,  (Ar) = 1.6411 Å 3,  (Ar-TiCl + ) = 26.99 amu, T = 208 K, P = 50 mTorr –v d = 458.8 m/s Doppler shift – –  = 606 kHz at v 0 = 396 GHz Line width:  ~ 1300 kHz Modulation index =  /  = 0.46 –Under-modulated at millimeter wavelengths

6. Source Modulation Velocity Modulation Source Modulation Velocity Modulation Source Modulation Velocity Modulation <5% leakage of neutral signals in VM mode Using Velocity Modulation Use velocity modulation to distinguish neutrals from ions

7. Past Studies of TiCl + Balfour & Chandrasekhar (1990) –First observed visible spectrum Kaledin & Heaven (1995,1997a,1997b) –Predicted X 3  r & confirmed using laser absorption Focsa et al. (1997a,1997b,1998,1999) –Used laser absorption/velocity modulation to measure several electronic transitions –Found that the  = 2 & 3 subbands of X 3  r perturbed by  3  r state –Established spectroscopic constants for each state

8. Gas-Phase Synthesis of TiCl + Add TiCl 4 –Pressure: <1 mTorr 20 mTorr Ar gas also added AC discharge –200 W at 600 

9. Energy Level Diagram for TiCl + 3  r ground state –Two unpaired 3d electrons J = L + S Spin-orbit and spin-spin interactions – & Omega ladders –  = 2, 3, 4 – J ≥  A 3  r state close in energy –Perturbs  = 2 & 3 ladders

10. Source Modulation Velocity Modulation Rotational Spectrum of TiCl + Fine structure components shifted from normal pattern TiCl + confirmed by VM –S/N down by factor of 4 Measured 37 Cl, 46 Ti isotopomers in natural abundance

11. Measured 10 rotational transitions of 48 Ti 35 Cl +, 48 Ti 37 Cl +, & 46 Ti 35 Cl + JJ J  obs obs - calc JJ J  obs obs - calc 30  312322927.414-0.01535  362374883.903-0.009 3323297.905-0.0893375315.2820.021 4323156.037-0.0814375163.2980.063 31  322333322.9600.01336  372385268.555-0.001 3333705.6630.0283385712.1310.015 4333561.278-0.0354385558.7870.053 32  332343716.4340.01537  382395650.832-0.001 3344111.2660.0203396106.617-0.007 4343964.669-0.0114395952.1030.025 33  342354107.777-0.00338  392406030.676-0.003 3354514.7880.0253406498.708-0.014 4354366.1900.0294406343.266-0.003 34  352364496.962-0.00339  402416408.0360.006 3364916.1430.0213416888.324-0.021 4364765.7530.0554416732.131-0.099 Rest Frequencies of 48 Ti 35 Cl + (X 3  r )

12. Spectroscopic Analysis of TiCl + Determined spectroscopic constants for TiCl + 48 Ti 35 Cl + ParameterMMWOptical B5216.6676(21)5226.07(54) D0.00256353(78)0.002728(45) A1900000 a 1904570(80) ADAD 2.7834(89)-0.489(54) AHAH 6.308(36) x 10 -5 4404278(5000)11030(180) D -18.071(46)0.507(18) H -1.000 x 10 -5 a rms0.037 a Held Fixed Rotational constants agree Fine structure parameters different –Different analysis methods reflects large perturbation from A 3  r state

13. TiCl vs. TiCl + Relative intensities of TiCl vs. TiCl + very similar Neutral only ~1.5x stronger than ion Ions usually very small fraction of plasma TiCl 4 produces ions well

14. Future Work Measure spectra of more titanium species & molecular ions –TiC (X 3   ), TiN + (X 1  + ), TiO + (X 2  r ), TiF + (X 3  r ) VCl - TH11 VCl + - TH12