Intracavity Laser Intracavity Laser Absorption SpectroscopyAbsorption Spectroscopy

of PtS in the Near Infraredof PtS in the Near Infrared

James J. O'BrienJames J. O'BrienUniversity of Missouri – St. LouisUniversity of Missouri – St. Louis

andandLeah C. O'Brien and Kimberly Handler

Southern Illinois University EdwardsvilleSouthern Illinois University Edwardsville

Previous Work on PtSPrevious Work on PtS 1995, Steimle Lab (ASU)

Three electronic transitions reported in the visible region Via LIF in a laser-ablation, molecular beam experiment The (0,0) band of the B – X and (0,0) and (1,0) bands of the

C – X transitions were recorded at high resolution and analyzed Observed states of PtS were assigned as X Ω=0, A Ω=1,

B Ω=0, and C Ω=0 Pure rotation spectrum of PtS also presented Later that year, the group reported the electric dipole moment

of PtS in the ground state

Li, Jung, & Steimle, J. Mol. Spec. 170, 310-322 (1995).Steimle, Jung & Li, J. Chem. Phys. 103, 1767-1772 (1995)

Previous Work on PtSPrevious Work on PtS 2004 Gerry Lab (UBC)

Pure rotational spectrum Examined several different istopologues of PtS Their results support a ground state with X 3Σ¯

0+ symmetry with Hund’s case (c) coupling, similar to PtO

Based on significant hyperfine and Born-Oppenheimer breakdown parameters

2009 Andrews Lab (U. Virginia)2009 Andrews Lab (U. Virginia) Infrared spectrum of PtS in a cryogenic matrixInfrared spectrum of PtS in a cryogenic matrix Weak vibrational bands of PtWeak vibrational bands of Pt3232S and PtS and Pt3434S at 491.7 and 479.3 S at 491.7 and 479.3

cmcm-1-1, respectively, respectively Density Functional Theory (DFT) calculations for the lowest Density Functional Theory (DFT) calculations for the lowest

singlet and triplet states of Ptsinglet and triplet states of Pt3232S gave vibrational frequencies S gave vibrational frequencies of 500.6 cmof 500.6 cm-1-1, in good agreement with the experimental results, in good agreement with the experimental results

Cooke & Gerry, J. Chem. Phys. 121, 3486-3494 (2004).Liang, Wang & Andrews, J. Phys. Chem. A, 113, 3336-3343 (2009).

Experimental ConditionsExperimental Conditions Used Intracavity Laser Absorption Used Intracavity Laser Absorption

Spectroscopy (ILS)Spectroscopy (ILS) Ti:sapphire laser: 11400 – 13500 cmTi:sapphire laser: 11400 – 13500 cm-1-1 range range ttgg ~ 100 ~ 100 μμsecsec

LLeffeff ~ 1 km ~ 1 km

Hollow Cathode SourceHollow Cathode Source 50 mm Pt-lined hollow cathode50 mm Pt-lined hollow cathode 0.5 Amp Discharge Current0.5 Amp Discharge Current ~ 2 Torr Argon + trace SF~ 2 Torr Argon + trace SF66

55

OC

HR = High ReflectorOC = Output Coupler

HR OC

LaserMedium

HR

LaserMedium

Absorber

LaserMedium

OCTuning ElementsHR

Measuring Absorption by Intracavity Laser Spectroscopy

Beer-Lambert Absorbance Relationship for ILS: When ILS laser observed at a well defined time after the onset of laser

operation, the averaged time-resolved spectrum (for initial 500 μs–1 ms) is:

Absorbance = ln [I0(ν)/I(ν)] = (ν) N [c • tg• l/L], where

I0(ν), I(ν) = laser intensity without and with absorption at frequency ν (ν) is the absorption coefficient at ν N = number density [ pressure or concentration] c is the speed of light = 3 x 108 meter/second tg is the generation time l/L is the fraction of cavity occupied by the absorber

i.e., Effective absorption pathlength (Leff) = c • tg • l/L

tg determines sensitivity (Leff =100 km for tg = 500 µs, l/L = 2/3), and permits a huge dynamic range because it can be easily altered

tg ~ 500 µs relatively easy for standing wave lasers; much longer times possible with special ring configured systems 1000’s miles of pathlength!

ILS Schematic DiagramILS Schematic Diagram

Intracavity Laser ChamberIntracavity Laser Chamber

2009 PtF Spectrum, RF012009 PtF Spectrum, RF01

Pt + SFPt + SF66

While recording and analyzing PtF spectra….While recording and analyzing PtF spectra…. Several bands looked different from those Several bands looked different from those

for PtFfor PtF Line spacing more denseLine spacing more dense Rotational structure looked like a singlet Rotational structure looked like a singlet

(whereas, PtF is a doublet)(whereas, PtF is a doublet) → → These bands cThese bands consistent with PtSonsistent with PtS

ResultsResults

Strong bandhead at 12460.5 cmStrong bandhead at 12460.5 cm-1-1

1 P-branch and 1 R-branch identified1 P-branch and 1 R-branch identified Branch structure consistent with 0Branch structure consistent with 0++ - 0 - 0++

transitiontransition No isotopologue structure of PtS was observedNo isotopologue structure of PtS was observed Conclusion:Conclusion:

(0,0) band of a newly identified [12.5] (0,0) band of a newly identified [12.5] =0=0++ – – XX =0=0++ of PtS of PtS

AnalysisAnalysis Used PtS constants from Cooke and Gerry (2004) to Used PtS constants from Cooke and Gerry (2004) to

calculate calculate ΔΔ22F valuesF values 66 R-lines and 45 P-lines and 66 R-lines and 45 P-lines and ΔΔ22F values to obtain secure F values to obtain secure

rotational assignmentrotational assignment ΔΔ22F(JF(J″″) = F(J) = F(J″″+1) – F(J+1) – F(J″″-1) = R(J-1) = R(J″″-1) – P(J-1) – P(J″″+1)+1)

Definitely PtS, lower state is v=0 of the Definitely PtS, lower state is v=0 of the XX 0 0++ state state Our observed J-values ranged from 7 to 90Our observed J-values ranged from 7 to 90 Ground state parameters were held fixed in fitGround state parameters were held fixed in fit 3 excited state parameters determined: E3 excited state parameters determined: E0000, B, B00 and D and D00

Average residual was ±0.005 cmAverage residual was ±0.005 cm‑1‑1, consistent with our , consistent with our estimated experimental accuracy for strong, non-blended estimated experimental accuracy for strong, non-blended lines (referenced to Ilines (referenced to I22 Atlas) Atlas)

Section of Section of PtS Lines, PtS Lines, Assignments Assignments and and ResidualsResiduals

J" R (J”) o-c P(J”) o-c 27 12460.2141 -0.0075 12444.7879 0.0036 28 12460.1194 -0.0035 12444.1278 0.0029 29 12460.0036 -0.0069 12443.4573 0.0054 30 12459.8810 -0.0037 12442.7800 0.0146 31 12459.7409 -0.0043 12442.0655 0.0001 32 12459.5860 -0.0061 12441.3517 -0.0002 33 12459.4141 -0.0114 12440.6243 -0.0006 34 12459.2437 -0.0016 12439.8791 -0.0053 35 12459.0619 0.0104 12439.1248 -0.0056 36 12458.8431 -0.0011 12438.3576 -0.0052 37 12458.6204 -0.0028 12437.5809 -0.0009 38 12458.3825 -0.0062 12436.7795 -0.0078 39 12458.1338 -0.0068 12435.9762 -0.0031 40 12457.8704 -0.0085 12435.1480 -0.0098 41 12457.5980 -0.0055 12434.3204 -0.0024 42 12457.3188 0.0042 12433.4697 -0.0046 43 12457.0085 -0.0037 12432.6243 0.0120 44 12456.6912 -0.0049 12431.7455 0.0087 45 12456.3662 -0.0002 12430.8620 0.0142 46 12456.0192 -0.0039 12429.9531 0.0077 47 12455.6424 -0.0239 12429.0391 0.0097 48 12455.2934 -0.0024 12428.1013 0.0013 49 12454.9095 -0.0022 12427.1636 0.0066 50 12454.5122 -0.0019 12426.2107 0.0101 51 12454.1058 0.0030 12425.2320 0.0013 52 12453.6792 0.0013 12424.2500 0.0027 53 12453.2421 0.0027 12423.2548 0.0044 54 12452.7856 -0.0017 12422.2390 -0.0011 55 12452.3200 -0.0016 12421.2184 0.0022

Observed J-values ranged from 7 to 90

Molecular Constants for PtS Molecular Constants for PtS (in cm(in cm-1-1))

E B0 D0 x108 r0 (Å)

[12.5] Ω=0 12457.4804(13) 0.140411639(88) 4.832(12) 2.091

X Ω=0 0.0 0.147180835a 4.8033a 2.042

aCooke and Gerry 20041σ given in parentheses

• Based on a Fenske-Hall calculation

• π2 configuration gives rise to the X 3Σ-

0,1 states

• 3σ to 4σ excitation would result in an excited 0+ state (from 3Σ-

0,1)

MO diagram for PtS

ConclusionsConclusions Recorded the 12460 cmRecorded the 12460 cm-1-1 band of PtS by ILS band of PtS by ILS (0,0) band of a 0(0,0) band of a 0++ - - XX 0 0++ transition transition Molecular constants for the excited state determined: EMolecular constants for the excited state determined: E0000, B, B00

′′

and Dand D00′′

NSF and PRF for financial supportNSF and PRF for financial support Kimberly Handler is an Kimberly Handler is an

undergraduate student at SIUEundergraduate student at SIUE

AcknowledgementsAcknowledgements