Intracavity Laser Absorption Spectroscopy of PtS in the Near Infrared James J. O'Brien University of Missouri – St. Louis and Leah C. O'Brien and Kimberly Handler Southern Illinois University Edwardsville

Previous 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, (1995). Steimle, Jung & Li, J. Chem. Phys. 103, (1995)

Previous Work on PtS 2004 Gerry Lab (UBC) Pure rotational spectrum Examined several different istopologues of PtS Their results support a ground state with X 3 Σ ¯ 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 matrix Infrared spectrum of PtS in a cryogenic matrix Weak vibrational bands of Pt 32 S and Pt 34 S at and cm -1, respectively Weak vibrational bands of Pt 32 S and Pt 34 S at and cm -1, respectively Density Functional Theory (DFT) calculations for the lowest singlet and triplet states of Pt 32 S gave vibrational frequencies of cm -1, in good agreement with the experimental results Density Functional Theory (DFT) calculations for the lowest singlet and triplet states of Pt 32 S gave vibrational frequencies of cm -1, in good agreement with the experimental results Cooke & Gerry, J. Chem. Phys. 121, (2004). Liang, Wang & Andrews, J. Phys. Chem. A, 113, (2009).

Experimental Conditions Used Intracavity Laser Absorption Spectroscopy (ILS) Used Intracavity Laser Absorption Spectroscopy (ILS) Ti:sapphire laser: – cm -1 range Ti:sapphire laser: – cm -1 range t g ~ 100 μsec t g ~ 100 μsec L eff ~ 1 km L eff ~ 1 km Hollow Cathode Source Hollow Cathode Source 50 mm Pt-lined hollow cathode 50 mm Pt-lined hollow cathode 0.5 Amp Discharge Current 0.5 Amp Discharge Current ~ 2 Torr Argon + trace SF 6 ~ 2 Torr Argon + trace SF 6

55 OC HR = High Reflector OC = Output Coupler HR OC Laser Medium HR Laser Medium Absorber Laser Medium OC Tuning Elements HR 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 [I 0 (ν)/I(ν)] =  (ν) N [c t g l/L], where I 0 (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 10 8 meter/second t g is the generation time l/L is the fraction of cavity occupied by the absorber i.e., Effective absorption pathlength (L eff ) = c t g l/L t g determines sensitivity (L eff =100 km for t g = 500 µs, l/L = 2/3), and permits a huge dynamic range because it can be easily altered t g ~ 500 µs relatively easy for standing wave lasers; much longer times possible with special ring configured systems  1000’s miles of pathlength!

ILS Schematic Diagram

Intracavity Laser Chamber

2009 PtF Spectrum, RF01

Pt + SF 6 While recording and analyzing PtF spectra…. While recording and analyzing PtF spectra…. Several bands looked different from those for PtF Several bands looked different from those for PtF Line spacing more dense Line spacing more dense Rotational structure looked like a singlet (whereas, PtF is a doublet) Rotational structure looked like a singlet (whereas, PtF is a doublet) → These bands consistent with PtS → These bands consistent with PtS

Results Strong bandhead at cm -1 Strong bandhead at cm -1 1 P-branch and 1 R-branch identified 1 P-branch and 1 R-branch identified Branch structure consistent with transition Branch structure consistent with transition No isotopologue structure of PtS was observed No isotopologue structure of PtS was observed Conclusion: Conclusion: (0,0) band of a newly identified [12.5]  =0 + – X  =0 + of PtS (0,0) band of a newly identified [12.5]  =0 + – X  =0 + of PtS

Analysis Used PtS constants from Cooke and Gerry (2004) to calculate Δ 2 F values Used PtS constants from Cooke and Gerry (2004) to calculate Δ 2 F values 66 R-lines and 45 P-lines and Δ 2 F values to obtain secure rotational assignment 66 R-lines and 45 P-lines and Δ 2 F values to obtain secure rotational assignment Δ 2 F(J ″ ) = F(J ″ +1) – F(J ″ -1) = R(J ″ -1) – P(J ″ +1) Δ 2 F(J ″ ) = F(J ″ +1) – F(J ″ -1) = R(J ″ -1) – P(J ″ +1) Definitely PtS, lower state is v=0 of the X 0 + state Definitely PtS, lower state is v=0 of the X 0 + state Our observed J-values ranged from 7 to 90 Our observed J-values ranged from 7 to 90 Ground state parameters were held fixed in fit Ground state parameters were held fixed in fit 3 excited state parameters determined: E 00, B 0 and D 0 3 excited state parameters determined: E 00, B 0 and D 0 Average residual was ±0.005 cm ‑ 1, consistent with our estimated experimental accuracy for strong, non-blended lines (referenced to I 2 Atlas) Average residual was ±0.005 cm ‑ 1, consistent with our estimated experimental accuracy for strong, non-blended lines (referenced to I 2 Atlas)

Section of PtS Lines, Assignments and Residuals Observed J-values ranged from 7 to 90

Molecular Constants for PtS (in cm -1 ) EB0B0 D 0 x10 8 r 0 (Å) [12.5] Ω= (13) (88)4.832(12)2.091 X Ω= a a a Cooke and Gerry σ given in parentheses

Based on a Fenske-Hall calculation π 2 configuration gives rise to the X 3 Σ - 0,1 states 3σ to 4σ excitation would result in an excited 0 + state (from 3 Σ - 0,1 ) MO diagram for PtS

Conclusions Recorded the cm -1 band of PtS by ILS Recorded the cm -1 band of PtS by ILS (0,0) band of a X 0 + transition (0,0) band of a X 0 + transition Molecular constants for the excited state determined: E 00, B 0 ′ and D 0 ′ Molecular constants for the excited state determined: E 00, B 0 ′ and D 0 ′ NSF and PRF for financial support NSF and PRF for financial support Kimberly Handler is an undergraduate student at SIUE Kimberly Handler is an undergraduate student at SIUE Acknowledgements