© 2009 sri international temperature dependence of the vibrational relaxation of oh( = 1, 2) by o,...

© 2009 SRI International

TEMPERATURE DEPENDENCE OF TEMPERATURE DEPENDENCE OF THE VIBRATIONAL RELAXATION OF THE VIBRATIONAL RELAXATION OF

OH(OH( = 1, 2) by O, O = 1, 2) by O, O22, AND CO, AND CO22

Constantin Romanescu, Henry Timmers, Gregory P. Smith, Konstantinos S. Kalogerakis, and Richard A. Copeland

SRI International, Molecular Physics Laboratory, Menlo Park, CA 94025


OH(OH() in the terrestrial atmospheres) in the terrestrial atmospheres

Source:

3 2( 5 9)O H OH O

Emission from OH() dominates the visible and infrared emissions of the atmospheric nightglow (Meinel bands).

Collisional energy transfer between OH() and other atmospheric species significantly influences the mesospheric heat budget.

1E10 1E11 1E12 1E13 1E1475

80

85

90

95

100

75

80

85

90

95

100

Thermosphere

Mesosphere

Alti

tude

, km

Colider density, cm-3

N2

O2

O-atoms

160 180 200 220 240

Temperature

Temperature, K


Why are we studying OH(Why are we studying OH( = 1 and 2)? = 1 and 2)?

0.0 0.2 0.4 0.6 0.8 1.0 1.260

70

80

90

100

110

120

2.51 - 3.14 µm (1 - 0)

Alt

itu

de

, Km

Emission rate, MR

150 200 250 300

Temperature

1.40 - 1.49 µm (2 - 0)

Ionosphere

Mesosphere

Troposphere

Temperature, K

Recent identification ofOH( = 1, 2) in the atmosphere of Venus requires a better understanding of the dynamics of the vibrational relaxation of OH by CO2;

Measurements for relaxation by CO2 at Venus mesospheric temperatures (T=160–200 K) are needed.

Venus temperature and OH( = 1, 2) emission rate vertical profiles (adapted from Piccioni et al., 2008)


GoalsGoals

Measure the vibrational relaxation rates of OH( = 1, 2) by O-atoms, CO2, and O2 at temperatures between160 – 300 K.

Estimate the = -1 / = -2 branching ratio for the vibrational relaxation of OH( = 2) by CO2.

Resolve the disagreement between the current literature values for the vibrational relaxation of OH( = 2) by O2 at room temperature.


Experimental approachExperimental approach

( )NascentOH

3

32

( ) ( ' 0.. 1)

( ) ( ' 0.. 1)

( )

O

M

r

k

k

k

O P O OH

OH M M OH

O P O H

13 2 2248

( )hnm

O O O D

1 32 2( ) ( )N O D N O P 1 2

2 ( ) 2 ( , 3)H O O D OH

1Time s

~10'Time s s

3 2 ( 5 9)O H O OH

collisionk

~100'Time s s


Vibrationally excited OH detectionVibrationally excited OH detection

318.0 318.5 319.0 319.5 320.0 320.5 321.0 321.5

Relative Inten

sity

Wavelength, Å

LIFBASE simulation

Experiment

OH A2+ - X2 (2,2) band

0.5 1.0 1.5 2.0 2.5 3.0 3.50

10000

20000

30000

40000

50000

60000

(1-1)

(2-2)

= 0

H + O(1D)

H + O(3P)

X 2

A 2+

Po

ten

tial e

ne

rgy,

cm

-1

O-H internuclear distance, Å318.5 319.0 319.5 320.0 320.5 321.0 321.5

OH A2+ - X2 (2,2) LIF excitation band

Q1(1)

Experimental

LIFBASE simulationT = 300K

OH

( =

2)

LIF

sig

na

l, a

.u.

Wavelength, nm

Excite the Q1(1) line of the diagonal bands of A – X transition;

Monitor the excited state population via the = -1 transition LIF.


Experimental set-upExperimental set-up

O3

Pump 1

Pump 2

Nd:YAG laser

Dyelaserl =248 nm

l =355 nm

Doubler

l =620-650 nm

UV monitor

Amplifier

l =310-325 nm

CO2, O2

Boxcar

PMT

Excimer laser

Hg lamp254 nm

30 cm f.l.

70 cm f.l.

Lab Computer

N2

Ar

Flowmeters

Ar

Ar

Ozonetrap

PMT

H2O


Vibrational relaxation of OH(Vibrational relaxation of OH( = 2) by O-atoms = 2) by O-atoms

0.6 11 3 1( 2) 0.97.3 10OH Ok cm s

11 3 1( 2) 8.6 1.0 10OH Ok cm s

T = 300K

T = 240K

First measurement of this rate constant at a lower temperature.

T = 210K11 3 1

( 2) 9.6 1.0 10OH Ok cm s

0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

OH

( =

2)

deca

y ra

te, µ

s-1

O-atom pressure, Torr

0 10 20 30 40 50 60

0.00

0.03

0.06

0.09

0.12

LIF

sig

nal,

a.u.

Pump-probe delay, µs


Vibrational relaxation of OH(Vibrational relaxation of OH( = 2) by CO = 2) by CO22 and O and O22

0 2 4 6 8 10 120.00

0.05

0.10

0.15

0.20T = 300 K

pO = 16.7 mTorr

pH

2O = 2 mTorr

pOH

= 50 µTorr (est.)

OH

( =

2)

de

cay

con

sta

nt,

µs-1

O2 pressure, Torr

2

13 3 1( 2) 4.3 0.5 10OH Ok cm s

2

13 3 1( 2) 8.4 1.0 10OH COk cm s

.

.. 1 21 87 9

.

.. 0 30 53 0

( )6.7 1.1 a ( )6.86 0.75 b ( )4.8 1.5 c( )2.6 0.54 a ( )1.1 0.3 d ( )2.7 0.8 c

Collider This work Previous resultsCO2

O2

Room temperature measurements (k x 10-13 cm3s-1)

T = 240K

(a) Rensberger et al., 1989.(b) Raiche, G. et al. 1990.(c) Dodd, J.A. et al. 1991.(d) D’Ottone, L. et al. 2004.

2

13 3 1( 2) 4.6 1.0 10OH Ok cm s

2

13 3 1( 2) 8.4 1.2 10OH COk cm s

T = 210K


Relaxation of OH(Relaxation of OH( = 2) – Temperature dependence = 2) – Temperature dependence

150 200 250 30010-13

10-12

Current work, = 1 Current work, = 2 Rensberger et al., 1989, , Dodd et al., 1991, Raiche et al., 1990 Previous SRI work = 1

= 2

= 3

OH() + CO2

Rat

e co

nsta

nt,

cm3 s-1

Temperature, K200 300 400

10-13

10-12

= 1

= 2

= 3

Current work, = 2 Rensberger et al., 1989, , Dodd et al., 1991, , D'Ottone et al., 2004 Previous SRI work McCabe et al., 2006

OH() + O2

Rat

e co

nsta

nt,

cm3 s-1

Temperature, K


OH(OH( = 1) room temperature relaxation data = 1) room temperature relaxation data

Collider This work Previous resultsCO2 (*)

O (**) ( )3.9 0.6 c. .4 6 0 2

( )1.8 0.5 a. .1 8 0 1 ( )2.18 0.5 b

0.66 0.10f

(*) rate constant x 10-13 cm3s-1; (**) rate constant x 10-11 cm3s-1

Experimental data for the relaxation of OH( = 1 and 2) by CO2 and O-atoms

(a) Dodd, J.A. et al. 1991.(b) Raiche, G. et al. 1990.(c) Khachatrian et al., 2005.

0 10 20 30 40 50

pO = 44 mTorr

pCO

2

= 0.0 Torr

Time, µs

pO = 14 mTorr

pCO

2

= 5.16 Torr

OH

( =

1)

LIF

sig

nal

, a.u

.

pO = 5 mTorr

pCO

2

= 4.26 Torr

CO2 Branching ratio


ConclusionsConclusions

We measured the removal rate constants of OH( = 2) by O-atoms, CO2, and O2 at T = 210, 240, and 300K;

We resolved the discrepancy between the removal rate constants of OH( = 2) by O2 at room temperature;

The extracted branching value, CO2, points to a

predominantly = -1 vibrational relaxation of OH( = 2).


AcknowledgementsAcknowledgements

Dr. Dušan Pejaković, SRI InternationalDr. Robert Robertson, SRI International

FundingFunding

This work is supported by the NASA Geospace Science and Planetary Atmospheres Programs

Participation of Henry Timmers was made possible through the NSF Research Experience for Undergraduate (REU) program.


Kinetic equationsKinetic equations

1 1 121 1 2

12

2

2

( 2) ( 2)

1 102 1

0

11 ( 1) ( 1)

12 ( 2) ( 2)

( 1) ( 1)

( 2) ( 2)

O OH O O C OH CO Ct t t

t

t

t

OH O O OH CO C

OH O O OH CO C

k p k pOH OH e f e e

OH OH e

k p k p

k p k p

The strong coupling between the nascent vibrational population ratio (f) and the branching ratios (i) does not allow for the fitting of both parameters;

Estimation of the nascent vibrational distribution for the actual experimental conditions is needed.


Vibrational quenching of OH(Vibrational quenching of OH( = 1, 2) = 1, 2)

21 22

( 2)

( 1)

( ) 2 ( , 3)H Ok

OH

OH

O D H O OH X

pf

p

( 2 )3 3

2 1

2 1 2 0

( 2) ( ) ( 1) ( )

; 0 0.56(*)

O OH Ok

O Or

OH O P OH O P

k

k k k

( 2) 22 2( 2) ( 1)

0 1.0

C OH COk

C

OH CO OH CO

1. OH(= 1, 2) nascent distributions

2. OH(= 2) cascading

3. OH(= 1) quenching( 1)

( 1) 2

3

2 2

( 1) ( ) ( 0)

( 1) ( 0)

OH O

OH CO

k

k

OH O P OH O

OH CO OH CO

(*) , Robertson and Smith, J. Phys. Chem. A, 2006 11 3 12 3.2 10rk cm s


Why are we studying OH(Why are we studying OH( = 1 and 2)? = 1 and 2)?

There is a disagreement in the OH( = 2) room temperature rate constants;

A better understanding of the vibrational relaxation pathways of OH( ≥ 2), i.e. single or multiple quanta energy loss, is needed for the analysis of the nightglow of the terrestrial atmospheres.

Current literature values for the relaxation of OH( = 2) by CO2 and O2

0

1

2

3

4

5

6

7

8

CO2

2. Dodd et al., 1991

1. Rensberger et al., 1989

3. Dodd et al., 1992

2. Raiche et al., 1990

1. Rensberger et al., 1989

OH

( =

2)

rem

ova

l rat

e x

1013

, cm

3 s-1

1 2 30

1

2

3

3. D'Ottone et al., 2004

O2


Additional plotsAdditional plots

0.00 0.02 0.04 0.06 0.08 0.100.00

0.05

0.10

0.15

0.20

0.25

0.30

T = 300 K T = 210 K

OH

( =

2)

de

cay

con

sta

nt,

µs-1

O-atom pressure, Torr

0.00 0.01 0.02 0.03 0.04 0.05 0.060.0

0.1

0.2

slope = 4.5 ± 0.3 Torr-1µs-1

O - atoms

Collider pressure, Torr

0 1 2 30.0

0.1

0.2

slope = (8.3 ± 0.7) x 10-2 Torr-1µs-1

T = 210 K

CO2

0 1 2 3 40.0

0.1

0.2

OH

( =

2)

deca

y ra

te, µ

s-1

slope = (2.1 ± 0.5) x 10-2 Torr-1µs-1

O2

© 2009 sri international temperature dependence of the vibrational relaxation of oh( = 1, 2) by o,...

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