The Pure Rotational Spectrum of TiCl+ (X3r) by Velocity Modulation Spectroscopy

DeWayne T. Halfen and Lucy M. Ziurys

Department of ChemistryDepartment of Astronomy

Steward ObservatoryArizona Radio Observatory

University of Arizona

June 21, 2004

Why Molecular Ions ?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+ CO+ CH +

SO+ HCO+ HOC+

H2D+ HCS+ N2H+

H3O+ CH2D+ HCNH+

HOCO+ H2COH+ HC3NH+

OH+ OH HCl+

ArH+ HBr+

• Neutral species dominate over ions

• Built a new spectrometer – uses Velocity Modulation– Ion selective technique

Velocity Modulation SpectrometerVelocity Modulation Spectrometer

Detector

RadiationSource

Gas Cell

Reactant

Characteristics of Velocity ModulationCharacteristics of Velocity Modulation

• Drift velocity of TiCl+

–

– E = 1.9 V/cm, (Ar) = 1.6411 Å3, (Ar-TiCl+) = 26.99 amu, T = 208 K, P = 50 mTorr

– vd = 458.8 m/s

• Doppler shift

–

– = 606 kHz at v0 = 396 GHz

• Line width: ~ 1300 kHz

• Modulation index = / = 0.46– Under-modulated at millimeter wavelengths

15.273

T

P

760876.13Ev

2/1d

c

vvδν d

0

413.38 413.40 413.42 413.44 413.46 413.48

Frequency (GHz)

Source Modulation

46Ti35Cl+ ( = 2)J = 38 39

Source Modulation

413.38 413.40 413.42 413.44 413.46 413.48

Frequency (GHz)

Velocity Modulation

46Ti35Cl+ ( = 2)J = 38 39

Velocity Modulation

412.76 412.78 412.80 412.82 412.84

Frequency (GHz)

Source Modulation

48Ti35Cl ( = 7/2)J = 41.5 42.5

Source Modulation

412.76 412.78 412.80 412.82 412.84

Frequency (GHz)

Velocity Modulation

48Ti35Cl ( = 7/2)J = 41.5 42.5

Velocity Modulation

382.56 382.58 382.60 382.62 382.64

Frequency (GHz)

Source Modulation

V35Cl ( = 0e)J = 38 39

Source Modulation

382.56 382.58 382.60 382.62 382.64

Frequency (GHz)

Velocity Modulation

V35Cl ( = 0e)J = 38 39

Velocity Modulation

• <5% leakage of neutral signals in VM mode

Using Velocity ModulationUsing Velocity Modulation

• Use velocity modulation to distinguish neutrals from ions

Past Studies of TiCl+Past Studies of TiCl+

• Balfour & Chandrasekhar (1990)– First observed visible spectrum

• Kaledin & Heaven (1995,1997a,1997b) – Predicted X3r & 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 X3r perturbed by 3r state

– Established spectroscopic constants for each state

Gas-Phase Synthesis of TiCl+Gas-Phase Synthesis of TiCl+

• Add TiCl4

– Pressure: <1 mTorr

• 20 mTorr Ar gas also added

• AC discharge – 200 W at 600

Energy Level Diagram for TiCl+Energy Level Diagram for TiCl+

• 3r ground state– Two unpaired 3d electrons

• J = L + S

• Spin-orbit and spin-spin interactions– &

• Omega ladders– = 2, 3, 4

– J ≥

• A3r state close in energy– Perturbs = 2 & 3 ladders

SLAH so SSH ss

0

100

200

300

400

500

600

700

En

erg

y (

cm

-1)

A3r

= 4

= 3

= 2: v = 0

= 1

= 2

= 3

X3r

395.945 395.965395.64 395.66Frequency (GHz)

396.095 396.115

48Ti35Cl+ (X3r): J = 37 38 = 2

= 4

= 3

Source Modulation

395.945 395.965395.640 395.660Frequency (GHz)

396.095 396.115

48Ti35Cl+ (X3r): J = 37 38 = 2

= 4 = 3

Velocity ModulationVelocity Modulation

392 393 394 395 396Frequency (GHz)

TiCl+ (X3r) = 2

= 3

= 4

48Ti35Cl+

J = 37 38

46Ti35Cl+

J = 36 37

48Ti37Cl+

J = 38 39

Rotational Spectrum of TiCl+Rotational Spectrum of TiCl+

• Fine structure components shifted from normal pattern

• TiCl+ confirmed by VM– S/N down by

factor of 4

• Measured 37Cl, 46Ti isotopomers in natural abundance

• Measured 10 rotational transitions of 48Ti35Cl+, 48Ti37Cl+, & 46Ti35Cl+

J J obs obs - calc J J obs obs - calc

30 31 2 322927.414 -0.015 35 36 2 374883.903 -0.009

3 323297.905 -0.089 3 375315.282 0.021

4 323156.037 -0.081 4 375163.298 0.063

31 32 2 333322.960 0.013 36 37 2 385268.555 -0.001

3 333705.663 0.028 3 385712.131 0.015

4 333561.278 -0.035 4 385558.787 0.053

32 33 2 343716.434 0.015 37 38 2 395650.832 -0.001

3 344111.266 0.020 3 396106.617 -0.007

4 343964.669 -0.011 4 395952.103 0.025

33 34 2 354107.777 -0.003 38 39 2 406030.676 -0.003

3 354514.788 0.025 3 406498.708 -0.014

4 354366.190 0.029 4 406343.266 -0.003

34 35 2 364496.962 -0.003 39 40 2 416408.036 0.006

3 364916.143 0.021 3 416888.324 -0.021

4 364765.753 0.055 4 416732.131 -0.099

Rest Frequencies of 48Ti35Cl+ (X3r)Rest Frequencies of 48Ti35Cl+ (X3r)

Spectroscopic Analysis of TiCl+Spectroscopic Analysis of TiCl+

•

• Determined spectroscopic constants for TiCl+

sssoroteff HHHH

48Ti35Cl+

Parameter MMW Optical

B 5216.6676(21) 5226.07(54)

D 0.00256353(78) 0.002728(45)

A 1900000 a 1904570(80)

AD 2.7834(89) -0.489(54)

AH 6.308(36) x 10-5

4404278(5000) 11030(180)

D -18.071(46) 0.507(18)

H -1.000 x 10-5 a

rms 0.037 a Held Fixed

• Rotational constants agree

• Fine structure parameters different– Different analysis

methods

• reflects large perturbation from A3r state

TiCl vs. TiCl+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

• TiCl4 produces ions well

406.023 406.043

-0.5

0.0

0.5

1.0

Frequency (GHz)393.456391.298

-0.5

0.0

0.5

1.0

394.554392.375

406.334 406.354 406.491 406.511

= 3 = 4

= 2

48Ti35Cl (X4r): J = 39.5 40.5

48Ti35Cl+ (X3r): J = 38 39

*

= 3/2

= 5/2

= 7/2 = 9/2In

tens

ity

(mV

)In

tens

ity

(mV

)

Future WorkFuture Work

408.78 408.80 408.82 408.84 408.86

Frequency (GHz)

TiN (X2+)N = 10 11

J = 10.5 11.5

J = 9.5 10.5

• Measure spectra of more titanium species & molecular ions– TiC (X3), TiN+ (X1+), TiO+ (X2r), TiF+ (X3r)

411.39 411.41 411.43 411.45 411.47

Frequency (GHz)

TiO (X3r)

J = 12 13 = 1e/f

* *

• VCl - TH11

• VCl+ - TH12