Sub-Doppler Jet-Cooled Infrared Spectroscopy of ND 2 H 2 + and ND 3 H + in NH Stretch Fundamental Modes Astronomical Molecular Spectroscopy in the Age of ALMA Illinois Symposium on Molecular Spectroscopy Champaign, IL June 18, 2014 Chih-Hsuan Chang and David J. Nesbitt JILA/Department of Chemistry and Biochemistry National Institute for Standards and Technology University of Colorado Boulder, CO Astronomical Molecular Spectroscopy in the Age of ALMA Illinois Symposium on Molecular Spectroscopy Champaign, IL June 18, 2014 Chih-Hsuan Chang and David J. Nesbitt JILA/Department of Chemistry and Biochemistry National Institute for Standards and Technology University of Colorado Boulder, CO JILA

Motivation NH 4 + as ubiquitous ion in aqueous acid-base chemistry NH 4 + (and isotopomers) as potential spectral carriers in Young Stellar Objects (YSO) H/D fractionation from isotopomeric molecular ion densities ALMA spectral search facilitated by high precision predictions from high resolution laboratory molecular spectroscopy NH 4 + as ubiquitous ion in aqueous acid-base chemistry NH 4 + (and isotopomers) as potential spectral carriers in Young Stellar Objects (YSO) H/D fractionation from isotopomeric molecular ion densities ALMA spectral search facilitated by high precision predictions from high resolution laboratory molecular spectroscopy

Tentative IR assignment of NH 4 + spectral features “Young Stellar Objects” Approximately 12,000 light-years away from Earth, in the constellation Sagittarius Tentative IR assignment of NH 4 + spectral features “Young Stellar Objects” Approximately 12,000 light-years away from Earth, in the constellation Sagittarius Astronomical Observations Gibb et. al. Astrophysical J. 536,347(2000) W. A. Schutte and R. K. Khanna, A&A, 398, 1049(2003) Gibb et. al. Astrophysical J. 536,347(2000) W. A. Schutte and R. K. Khanna, A&A, 398, 1049(2003) NH 4 +

4 ND n H 4-n + Isotopomer Vibrations Jacox and Thompson, PCCP, (7) 765, 2005 Intensity in unit of km/mol. Oka group Saykally group Oka group Saykally group Nakanaga and Amano Park et. al.(1996)

Frequency stabilities  Polarization-stabilized HeNe laser Single mode scanning  1-2  m (DFG), 2-4  m (DFG), 4-10  m (QCL) Concatenation/calibration  Ultrastable servo-loop locked transfer cavity Frequency stabilities  Polarization-stabilized HeNe laser Single mode scanning  1-2  m (DFG), 2-4  m (DFG), 4-10  m (QCL) Concatenation/calibration  Ultrastable servo-loop locked transfer cavity Sub-Doppler Slit-Jet Spectrometer

Chemical reaction route : H 2 + e -  H e - H H 2  H H H ND 3  ND 3 H + + H 2 H ND 2 H  ND 2 H H 2 Chemical reaction route : H 2 + e -  H e - H H 2  H H H ND 3  ND 3 H + + H 2 H ND 2 H  ND 2 H H 2 Molecular Ion “Synthesis” Advantages:  Sub-Doppler resolution  Rovibrational cooling (30-40 K for ions)  High ion (10 12 #/cm 3 ) densities Advantages:  Sub-Doppler resolution  Rovibrational cooling (30-40 K for ions)  High ion (10 12 #/cm 3 ) densities mirror mirror Slit jet

NH Stretch Vibrational Band Types NH 2 D 2 + and ND 3 H + NH Stretch Vibrational Band Types NH 2 D 2 + and ND 3 H + NH 2 D 2 + ND 3 H +

Jet-Cooled ND 3 H + Spectral Data: Q-branch Region (  K = 0) Jet-Cooled ND 3 H + Spectral Data: Q-branch Region (  K = 0)

Sample P/R-Branch Data ND 3 H + NH Stretch (v 1 ) Sample P/R-Branch Data ND 3 H + NH Stretch (v 1 ) P-branch R-branch

Boltzmann Analysis and ND 3 H + Nuclear Spin Statistics Boltzmann Analysis and ND 3 H + Nuclear Spin Statistics K=3:K=1,2:K=0 g ns = 22:16:11 K=3:K=1,2:K=0 g ns = 22:16:11 ND 3 H + Nuclear spin modifications: K = Mod3 (K = 3n, n = 0 “special”) and K = 1,2, 4,5, 7,8… Boltzmann fits yield a well defined common rotational temperature (33 K) Spin populations from relative intercepts: 21.5(8):14.9(8):11.0(9) Consistent with 22:16:11 nuclear spin weights! Nuclear spin modifications: K = Mod3 (K = 3n, n = 0 “special”) and K = 1,2, 4,5, 7,8… Boltzmann fits yield a well defined common rotational temperature (33 K) Spin populations from relative intercepts: 21.5(8):14.9(8):11.0(9) Consistent with 22:16:11 nuclear spin weights!

Sample ND 2 H 2 + Data NH Asymmetric Stretch (v 6 ) Sample ND 2 H 2 + Data NH Asymmetric Stretch (v 6 )

ND 2 H 2 + Q branch (b-type) Symmetric NH Stretch (v 1 ) ND 2 H 2 + Q branch (b-type) Symmetric NH Stretch (v 1 ) (  K a = -1) (  K a = +1)

Relative Band Intensities |  c /  b | = 1.34(5) |  c /  b | 2 = 1.8(1) Good qualitative agreement with simple “bond-dipole” model predictions (2:1)

Preliminary Spectral Fits ND 3 H + B” = (30) cm -1 B’ = (82) cm -1 C’ – C” = cm -1 0 = (19) cm -1  ” = cm -1 B” = (30) cm -1 B’ = (82) cm -1 C’ – C” = cm -1 0 = (19) cm -1  ” = cm -1 ND 2 H 2 + (in cm-1) A” = (4) A 1 = (4) A 6 = (4) B” = (4) B 1 = (6) B 6 = (2) C’” = (6) C 1 = (4) C 6 = (2)  1 = (1) 6 = (1)  ” = cm -1  1,6 = cm -1 (in cm-1) A” = (4) A 1 = (4) A 6 = (4) B” = (4) B 1 = (6) B 6 = (2) C’” = (6) C 1 = (4) C 6 = (2)  1 = (1) 6 = (1)  ” = cm -1  1,6 = cm -1

Summary Slit jet supersonic discharge expansions as intense sources of jet- cooled molecular ions for universal, sub-Doppler, direct absorption molecular spectroscopy High resolution jet-cooled spectra of NH stretch modes of ND 3 H + ( 1 ) and ND 2 H 2 + ( 1, 6 ) observed, assigned and analyzed for the first time Boltzmann analysis permits direct measurements of cold rotational temperatures and nuclear spin statistics Relative band intensity of v 1 and v 6 modes consistent with simple “bond-dipole” physical picture High resolution data available for “bootstrapped” detection of H/D isotopomeric ammonium ions in the interstellar medium via mm/sub- mm array telescopes Slit jet supersonic discharge expansions as intense sources of jet- cooled molecular ions for universal, sub-Doppler, direct absorption molecular spectroscopy High resolution jet-cooled spectra of NH stretch modes of ND 3 H + ( 1 ) and ND 2 H 2 + ( 1, 6 ) observed, assigned and analyzed for the first time Boltzmann analysis permits direct measurements of cold rotational temperatures and nuclear spin statistics Relative band intensity of v 1 and v 6 modes consistent with simple “bond-dipole” physical picture High resolution data available for “bootstrapped” detection of H/D isotopomeric ammonium ions in the interstellar medium via mm/sub- mm array telescopes

Thanks! Chih-Hsuan Chang Fang Wang Melanie Roberts (SUNY) Chris Carpenter Chih-Hsuan Chang Fang Wang Melanie Roberts (SUNY) Chris Carpenter NSF DOE NIST NSF DOE NIST A great place to do molecular spectroscopy! (and physical chemistry!) A great place to do molecular spectroscopy! (and physical chemistry!)