Transcript ohiostatetalk2.pptx

Saturation of the NO2 ν1+ν3 and
the CH4 ν3 Transitions in Helium
Nanodroplets
Robert Fehnel
Kevin Lehmann
Department of Chemistry
University of Virginia
Why study Saturation of CH4 and NO2?
• By studying the saturation of these molecules we will
try to understand the line shapes in nanodroplets
which are inhomogenous.
• By studying relaxation we can try and find the
inhomogenous relaxation rates
• Try and understand the relationship between the
molecules and a superfluid
Machine Schematic
He
IR OPO
2560 – 3125 cm-1
Closed Circuit
Refrigerators
Multipass Cell
Nozzle
LHe
Chopper
Skimmer
Nozzle Diameter = 10 μm
Skimmer = 400 μm
Nozzle T ≥ 16 K
Backing Pressure ≤ 60 Bar
>5000 L/s
Pickup cell
1.5K bolometer
N.E.P.
~ 2x10-14 W/Hz1/2
2500 L/s
10
20
30
45 cm
Bolometer noise ~ beam noise ~ 10-5 of chopped beam signal(1 Hz BW)
Acculight Argos OPO
Approximately 1.75
W of power
measured entering
the polarizer and
upwards of 0.7W
entering the
spectrometer.
To Spectrometer
MgF2 Polarizer
S P
Wavemeter
150 MHz
I
7.5 GHz
etalon
OPO
etalon
Power
meter
Produces over 2 W of CW over the tunable range of 3.2 – 3.9 μm. Continuous scans
of 45 GHz. Also produces 2 - 5 W of 1.5 μm light.
Perry cell
Lens
Power Meter
He Beam
The Focal Spot was
determined to be 27 µm
in diameter. Peak
power is equal to 240
kW/cm2
Perry Cell Measurements I
Perry Cell Measurements 2
Beam Quality Singe Pass
R2 = 0.9898
Beam Quality Multi Pass
R2 = 0.98015
NO2 spectrum in He~5000
NO2 v1 + v3 R(0) ->
.
NO2 Signal vs Power
The R(0) Line is found at
2905.566 cm-1 and the FWHM
is 0.035 cm-1.
NO2 Signal vs Power
NO2 Signal vs Power
S = a*P/(1+P/Ps)
a = 58.954
Ps = 0.527
(Χ2/(Np-2))½ = 0.451
NO2 Signal vs Power
S = a*P/(1+P/Ps)
a = 58.954
Ps = 0.527
(Χ2/(Np-2))½ = 0.451
S = a*I/((1+P/Ps)½)
a = 68.751
Ps = 0.117
(Χ2/(Np-2))½ = 0.651
NO2 Widths
NO2 Widths
Δν = Δν0((1+I/Is)½)
Homogenous Case
Is = 150 kW/cm2
Δν0 = 0.033
(Χ2/(Np-2))½ = 1.9 x10-3
Methane R(0) Line
The R(0) Line is found at 3029.07 cm-1
and the FWHM is 0.20 cm-1.
Methane Signal vs Power
Methane Signal vs Power
S = a*P/(1+P/Ps)
a = 41.713
Ps = 0.458
(Χ2/(Np-2))½ = 0.152
Methane Signal vs Power
S = a*P/(1+P/Ps)
a = 41.713
Ps = 0.458
(Χ2/(Np-2))½ = 0.152
S = a*P/((1+P/Ps)½)
a = 49.723
Ps = 0.1
(Χ2/(Np-2))½ = 0.184
Methane Widths
Methane Widths
Δν = Δν0((1+I/Is)½)
Homogenous Case
Ps = 0.458
Δν0 = 0.172
(Χ2/(Np-2))½ = 1.7 x10-3
Results
NO2
CH4
Is (kW/cm2)
150
130
Transition
Dipole (D)
T1T2 (ns2)
T1 (ns)
0.05
0.057
0.31
1.0
0.26
5.0
T1T2 = (hbar*ε*c)/(2*μ*Is)
Results II
• Knowing that the focal point diameter is 27 µm
and the speed of the beam is 450 m/s then we
can determine that the NO2 spends 60ns in
each crossing with the beam
• We believe that by comparing our T1 time for
methane of 5 ns to a previous result by
Momose’ group for the v4 R(0) line of methane
which results in a 3.7 ns T2 time that we are
relaxing to the 2v4 and then to the ground state
Conclusions
• We were able to show saturation with both
CH4 and NO2
• With both species a homogenous and
inhomogenous fit worked well for signal
• Only homogenous line shape fit the widths
correctly
Future Work
• This technique could be applied to other
similar molecules with similar strong lines
such as CH3Cl and Propyne
• Also try to adjust the number of passes while
keeping the amount of scattered light low
– This could be done by putting the Perry cell on a
rotation stage
– Also determine saturation by number of passes
instead of using polarizer to adjust power
Acknowledgements
• Dr. Ozgur Birer who help construct the
HENDI machine at UVa.
Funding:
• National Science Foundation, UVa