1. 1 OBSERVATION OF TWO  =0 + EXCITED ELECTRONIC STATES IN JET-COOLED LaH Suresh Yarlagadda Ph.D Student Homi Bhabha National Institute Bhabha Atomic Research Centre Mumbai, India The 69 th International Symposium on Molecular Spectroscopy June 16-20, 2014

2.  Introduction  Experimental  Laser-induced fluorescence spectroscopy of LaH Molecules  Results and discussion  Summary Outline 2

3. 3 Introduction  Ground state symmetry was not confirmed experimentally  Missing energy linkage between singlet and triplet manifolds  Low-lying electronic states  High-lying excited electronic states La(a 2 D,5d 1 6s 2 )+H( 2 S) ???  LaH Molecule *KK das and Balasubramanian, CPL 172, 372 (1990)

4. Schematic of Experimental Setup LIF / TOFMS 10 -7 mbar La Metal rod Pulse Valve Ablation source Delay/Pulse Generator Pulse Valve Driver Nd-YAG Laser Excime r Laser Dye Laser Boxcar integrat or Mono- chromator Supersonic Molecular Beam HV Pulse He + 2% NH 3 (250kPa ) Sequence of the various events in the experiment Pulse Valve Ablation Laser Excitation laser 280  s 25  s (FJ) 4 LIF TOF-MS Ablation Laser To high-speed pumps 10 -5 mbar 10 -7 mbar PI Signal Ion-Optics LPI LIF Signal Mono PZT pulse valve He +3%NH 3 (250kPa)

5.  Electronic transitions of LaH molecules were first observed by A. Bernard and R. Bacis in visible region 3  - 3 ∆, 1    and  1 ∆- 1  Ground state as 3 ∆  High level ab initio calculations by K. K. Das and K. Balasubramanian predicted 1  as the ground state with low-lying 3 ∆ as the first excited state  Latter R. S. Ram and P. F. Bernath observed A 1  -X 1  and d 3  -a 3 ∆ of LaH. They reassigned the 1    and  1 ∆- 1  observed by Bernard as 0 + - a 3 ∆ and 3  2 - 3 ∆ 1 Based on abinitio calculation they assigned 1  as a ground state. In the absence of intercombination transition they could not establish singlet- triplet interval. LaH molecules were formed in the free-jet by reaction of laser produced Lanthanum metal plasma with 3% ammonia seeded in helium gas 5 Lanthanum Hydride (LaH) Molecules

6. 6 Our previous work on LaH Molecule Experimental confirmation of 1  + symmetry for the ground state Six new excited electronic states, one with Ω = 0 and five with Ω= 1 observed and rotationally analyzed in the visible region Observation of inter-combination transition 0 + ( 3   )-X 1   at 15622 cm -1 Established the missing energy linkage between singlet and triplet manifold Observed new low-lying excited electronic states i.e. 3  1,2, 3  0,1,2 and 1  2 The 3  state was predicted to be inverted but observed as regular Vibrational constants of the X 1  + ground state  e = 1418.2 (2) cm -1,  e x e = 15.6 (7) cm -1 were determined

7. 7 Observation & Assignments of new  = 0 + excited electronic states  Rotationally resolved laser-induced fluorescence excitation bands involving two excited electronic states at 21970.71 and 22100.31 cm -1 are observed  Both the bands are assigned based on observation of number of branches, combination differences for the lower state and radiative lifetimes R(J-1)-P(J+1) =F”(J-1)-F”(J+1) = 4B”(J+1/2)-8D”(J+1/2) 3 =   F”(J)  21970 and 22100 cm -1 bands originated from =0 of the X 1  + confirmed by Combination Differences(CD) J J-1 J+1 R(J-1) P(J+1) J

8. 8 Rotationally resolved new  = 0 + excited electronic states Rotational structure of Ω=0 + excitation bands of jet-cooled LaH molecule at 21970 and 22100 cm -1. Lanthanum atomic lines (La I) indicated by *. The simulated spectrum (inverted) was generated with derived molecular constants in Table, a spectral line width of 0.15cm -1 and an estimated rotational temperature of 120K.

9. 9 Molecular constants for new excited electronic states  The observed rotational lines were fitted in following expressions for the excited states with Ω=0 + for determining molecular constants  Hamiltonian for state with X 1  + and Ω = 0 : Molecular constants (in cm -1 ) for the 21970 and 22100 cm -1 bands ConstantsBand at 21970 cm -1 Band at 22100 cm -1 Tv 21970.71(2) 22100.31(3) Bv3.5065(15)3.2899(45) D v  10 4 -4.44(28)-52.03(163) H v  10 5  -3.8(2) L v  10 7  1.122(76) Fitting error(No. lines) 0.03(13) 0.06(21)  (ns)37.1(38)39.5(22)

10. 10 Dispersed Fluorescence spectra of two  = 0 + exited bands  Both the bands are weak in intensity while the monochromator was parked at the excitation laser wavelength  Strong fluorescence to =1 of the b 3  1 state displaced by about 5066 cm -1 from the laser line  Both bands shows transitions to mainly triplet states  Both states having short radiative lifetime  40 ns  The probably assignment is  = 0 + in Hund's case (c), as usual for heavy molecules  No theoretical predictions are available for these new electronic states

11. Electronic states of LaH Molecules 11

12. 12 Summary Two new excited electronic states of LaH were identified at T 0 =21970.7 and 22100.3 cm -1 in rotationally resolved laser-induced fluorescence jet-cooled excitation spectra The observation of a single P- and R-branch structure in both the bands originating from = 0 of X 1  + ground state confirms  = 0 + for both the excited states The molecular constants for both the excited states were determined using Pgopher programme

13. 13 Thank You Acknowledgments Dr. S.G Nakhate (Ph.D supervisor) Dr. Soumen Bhattacharyya Mr. Sheo Mukund Travel financial assistance by 1.Homi Bhabha National Institute (HBNI) 2.Departments of Science and Technology (DST) 3.Centre for International Co-operation in Science (CICS)