Daisuke Ando, * Susumu Kuma, ** Masaaki Tsubouchi,** and Takamasa Momose** *Kyoto University, JAPAN **The University of British Columbia, CANADA SPECTROSCOPY OF COLD MOLECULES PRODUCED BY VELOCITY FILTERING

What is “Cold molecules”? Both internal and translational energies (TE) are cold.  Supersonic expansion  Internal energies  O  TE in Lab. frame  X  By using slow molecules… 2. Reaction dynamics in low temperature collision 1. Ultra high precision spectroscopy Spectroscopy of bio-molecules Detection of internal dynamics from linewidth Interference of de Broglie wave Resonances at the intermediate state very difficult h t t fastslow

Buffer gas cooling e.g. Doyle (Harvard) Rapidly rotating source  Mechanical deceleration e.g. Herschbach (Harvard) Gas Stark effect  Stark deceleration  by using  time-varying electric fields e.g. Meijer (Max-Planck Institute)  Stark velocity filtering Our method     time Cryostat thermalization He  1 K Target molecules Generation of Cold Neutral Molecules rotating

Purpose of this Study Generation of slow molecules by Stark velocity filtering technique Observation of cold Molecules by LIF Spectroscopy

Fast molecules velocity Velocity Filtering Cold molecules exist even at room temperature. How can we realize such potential for neutral molecules ? Slow molecules

KM < 0 (Low-field seeker), Symmetric top molecules in the static electric filed E, Stark-Potential Barrier V Stark  E E position x 0 V Stark x position 0

Quadrupole Rempe (Max-Planck Institute)     Hexapole Large width of low filed region  High transmission Small width of low filed region  Low transmission Multipole Electrodes position V Stark x x 00 Linear potential Harmonic potential Trajectory can be stabilized near the potential minimum.   

To determine velocity distribution f(v), Time-of-flight (Nozzle to detector) was measured. Sample Benzonitrile Large dipole moment (  = 4.14 Debye)     4.0 mm 2.0 mm HV =  5 kV E max = 38 kV / cm Experimental Detail  10  9 Torr L = 1 m N Effusive beam Ionization detector Pulsed nuzzle

S(t) (10 3 cm -3 ) The most probable velocity = 20 m/s (  5 K) flight-time (ms) Result of Time-of-flight measurement : HV ON : HV OFF velocity (m/s) Flux (L = 1 m)

Centrifugal force F C = mv 2 / R < Stark force F Stark Centrifugal Force Dependence : R = 75.0 mm : R = 12.5 mm Small R Small v V Stark x position R flux velocity (m/s) The most probable velocity: 5 m/s (  0.3 K) (R =12.5 mm) 20 m/s (  5 K) (R =75.0 mm) Flux: 4  10 8 s -1 (R =12.5 mm) 14  10 8 s -1 (R =75.0 mm)

Summary of Velocity Filtering We have successfully produced cold molecular beams at 0.3 K using a hexapole Stark velocity filter. Sample /  VelocityTemp.RE In this workBzCN / 4.1 D 5 m/s0.3 K12.5 mm 38 kV / cm 20 m/s5 K75.0 mm RempeND 3 / 1.5 D40 m/s4 K12.5 mm90 kV / cm KanamoriND 3 / 1.5 D120 m/s35 K135 mm90 kV / cm

Rotational distribution of Cold Molecules Stark energy: Threshold velocity depends on rotational levels. Rotational state distribution should be changed by velocity filtering. The rotational distribution is completely non-equilibrium distribution. velocity (m/s) (J KaKc, M) =(20 17, 4, -18) (J KaKc, M) =(46 17,29, -40) (J KaKc, M) =(56 32,25, -38) f(v)f(v) guided filtered

Calculation: 0-0 band of S 1 - S 0 LIF Spectra of BzCN Drastic change is predicted in the calculated LIF spectrum. 300 K 0.3 K filtered Wave number (cm -1 ) Fiber Spectrum of cold beam has not been obtained yet. Molecules in cold beam occupy many rotational quantum numbers. The number density per quantum number is not large enough to detect signals.

Future Plans AOM IR Laser Stabilization High-flux cold molecular source Cryostat Infrared Cavity Decelerator Ultra cold regime in the mK He buffer gas cooling (4 K) The number density of single quantum number increase drastically Kuma, Momose APS / DAMOP 2007

The resultant force on the molecule depends on…  dW / dE    E A polar molecule is affected with Stark effect through electric fields (E).  Stark energy = W Stark (E) In inhomogeneous electric fields(E), a polar molecule have Stark force  Stark force = +5kV  5kV F   Stark force

    kVolt / cm 50 0 55 55 5 5 mm Cross section of a guide A B section A-B E (kV / cm) Stark energy (cm -1 ) Potential energy for ND 3 in the |J K M> = |1 1 -1> Velocity distribution of the guided molecules Velocity (m/s) Guide: Quadrupole electrode Previous Work

Stark energy (cm -1 )  Almost harmonic potential  Large section area of hexapole  High transmission Potential energy for ND 3 in the |J K M> = |1 1 -1>       kVolt / cm 50 0 mm 55 55 5 5 A B section A-B E (kV / cm) Cross section of a guide Guide: Hexapole electrode In this work

Spectroscopic Properties BzCN at 300 K Guided BzCN (  0.3 K ) BzCN at 1 mK Doppler width ( at cm -1 ) ( at cm -1 ) 1450 MHz 73 MHz 46 MHz 2.3 MHz 2.6 MHz 0.1 MHz Transit-time width d = 1mm 1.2 MHz39 kHz2.3 kHz dB 18 pm0.6 nm10 nm 10 MHz cf. Molecular beam Cold molecular beams of 1 mK  Spectral resolution of  10 kHz

|J,Ka,Kc,M> = |0,0,0,0> |J,Ka,Kc,M> = |1,0,1,0> |J,Ka,Kc,M> = |2,0,2,0> |J,Ka,Kc,M> = |3,0,3,0> |J,Ka,Kc,M> = |2,2,1,0> |J,Ka,Kc,M> = |2,2,0,0> |J,Ka,Kc,M> = |4,0,4,0> |J,Ka,Kc,M> = |3,2,2,0> Calc: Stark Energy