Molecular pairs in the atmosphere,the carriers of continuum-like

absorption

Andrei A. VigasinAndrei A. Vigasin

General Physics & Atmospheric PhysicsInstitutes,

Russian Academy of Sciences,Moscow

CAVIAR meeting, London, 2008

Water vapor continuum absorption

, cm-1

Water vapor continuum absorption(after Baranov, 2008)

Near surface downwelling radiation flux (for the Standard Tropical Atmospheric profile)within the wavelength range from 2000 to 3200 cm-1 is ~1.5 times in excess of thatcalculated using the MTCKD-2.1 continuum model [estimated by B. Fomin, 2008].

Terrestrial Terrestrial radiationradiationpeaks herepeaks here

Solar radiation peaks Solar radiation peaks therethere

To avoid continuouscontroversy it looksrational to start AB OVO

Monomer far wings or water dimers?

The war between the two countries is over the BigEnded and the LittleEnded controversy which is a debate over which end an egg should be cracked...after Jonathan Swift, Gulliver's Travels

One has to define without ambiguity whatmust be called true dimers or colliding pairs and how to distinguish among them Partitioning of pair states as a function of

temperature

Classical trajectory analysis in the phase space

Collision-induced intensity and its T-dependence

Temperature effect on the water vapor continuum

The real gas virial equation of state

Interaction induced correction to unimolecular absorption

Interaction induced correction to unimolecular absorption

Linear term vanishes in case of dipole forbidden transitions(highly symmetrical molecules such as N2, O2, CO2 etc.).

Quadratic term (binary absorption coefficient) implies the aggregateeffect of the totality of pair states in a gas, no matter be it true dimer,quasibound, or free state.

To reveal partial effect of a selected group of pair states (e.g. dimeror whatever) one has to learn how to partition the phase space oftwo interacting species.

Bound, quasibound, and free pair states

Ueff = U(r) + h L(L+1)

82cr

Phase space subdivision forstructureless monomers

End-over-end rotational energy

Tra

nsla

tion

al k

inet

ic e

nerg

y

Metastable

Free pairs

Truebound

EL

EL

ER

EiEi

No matter what intermolecular pairNo matter what intermolecular pair

ER EL Ei

222

22

211

21

2102

22

22),,,()(

22 rm

J

rm

JRVRV

R

LpH R

The use of kinetic energy termsto subdivide the phase space

Partitioning in the phase spaceof polyatomic dimers

The Ar-CO2 system

Potential Energy Surface

Ab initio PES from …….J. Hutson et al., J. Chem.Phys., 105, 9130 (1996).

Typical trajectories showing the difference among free and

quasibound pair states

Quasicomplex formation Free pair state

TIME

Classical 3D trajectory analysis of the Ar-CO2 pair states

Projections of two slices across Ei onto (ER, EL) planeat selected separation R

S. Lokshtanov, S. Ivanov, and A. Vigasin J. Molecular Structure, 742, 31 (2005).

Collision-induced absorption in the region of the CO2 Fermi dyad

A. Vigasin,Y. Baranov, and G. Chlenova J. Molecular Spectroscopy, 213, 51 (2002).

Normalized collision-inducedintensity in the Fermi dyad

and triad ranges

Collision-induced absorption in theN2 fundamental

T = 343 K

O-branch

Q-branch

S-branch

True dimer absorption is buried here and only here

Ripple structure is OUT-OF-PHASEwith N2 rotationallines!

Y. Baranov, W. Lafferty, and G. Fraser, J. Molecular Spectroscopy, 233, 160 (2005).

Normalized contributions to CIA intensity in the N2 fundamental

The result of Monte-Carlo 11-fold integration of the ab initio calculated [at CCSD(T) level of theory] induced dipole over pre-selected domains in the phase space

S. Lokshtanov and A. Vigasin, 2008, to be published

Temperature variations of the CIA intensity in the N2 fundamental

Temperature variations of the CIA intensity in the N2 fundamental

Temperature variations of the CIA intensity in the N2 fundamental

Integrated CIA intensityis calculated usingab initio PES(Van der Avoird e.a., 1984),CCSD(T) dipole surface and classical integration

S. Lokshtanov, B. Bussery-Honvault,and A. Vigasin, Molecular Physics,106, 1227 (2008).

Temperature variations of theCIA intensity in oxygen

50 100 150 200 250 300 350 4000,9

1,0

1,1

1,2

1,3

No

rma

lize

d C

IA In

ten

sity

T, K

O2-O

2

FundamentalBaranov e.a., 2004

Herzberg III

X3-

g A3

u (203 nm)

Zelikina e.a., 2005

See also….Ubachs e.a., JQSRT, 2006

Drastic effect of close collisionson induced dipole

Low temperature limit:Bab ~ |(Re)|2 x exp(-De/kT)

Re

De

(Re)

Drastic effect of close collisionson induced dipole

High temperature limit:

Bab ~ kT

Temperature dependence of the water vapor continuum absorption (near 944 cm-1)

(at 1200 cm-1)

Temperature dependence of continuum at 944 cm-1, CRDS

(from Cormier et al., JCP, 2005)

H2O-H2O

Dimer modelVigasin, JQSRT, 2000

Far wing

De = -15.7 kJ/mole

VRT(ASP-W)IIIGoldman e.a., JPC, 2004

-1/2

Temperature dependence of the continuum binary absorption coefficient

(Baranov et al., 2008)

1.00

1.50

2.00

2.50

3.00

3.50

2.40 2.60 2.80 3.00 3.20 3.40

ln(C

s*1

023)

850 cm-1

944 cm-1

1100 cm-1

1200 cm-1

The first and the last big figures arereproduced from AFGL-TR-81 (Burch D. E.)

0.30

0.80

1.30

1.80

2.30

2.80

3.30

2.60 2.80 3.00 3.20 3.40

ln(C

s*1

023)

1930 cm-1

1973 cm-1

2050 cm-1

2143 cm-1

Temperature, 1000/Θ, K-1 Temperature, 1000/Θ, K-1

The fraction of true bound orquasibound pair states

in the water vapor

This ratio of partition functions was calculated previously after pair statespartitioning in the phase space.

Here Kpbound(T) stands for the true bound dimers equilibrium constant;

True dimer absorption cross-section bound() is evaluated fromanharmonic variational calculations;

Metastable dimer cross-section metastable() can be taken as doubledand broadened monomer cross-section: 2 monomer();

Binary absorption coefficient in a mixture of true bound and metastable dimers

Variational anharmonic calculations of the far IR water dimer spectrum

CKD

Water dimer

End-over-endrotation

Intermolecular fundamentals

Intermolecular overtones and combination bands

A. Pavlyuchko and A. Vigasin, 2008, to be published

(Kp = 0.04 atm-1)

Vibrational problem:Vibrational problem:B3LYP/6-311G(3df,3pd) method is used to find trial harmonic or Morse potential parameters.These parameters are adjusted to meet the water dimer intermolecular fundamentals measured in the Ne matrix.Variational solution is found then with 18564 functions in the basis set.

Rovibrational problem:Rovibrational problem:Variational basis set consists of the direct product of vibrational and Wigner functions. Maximum basis set at J = 10 consists of 40887 functions.

Intensities:Intensities:Dipole function (as well as its first and second derivatives) is found with the use of ab initio calculations at MP2/6-311G(3d,2p) level.

Average density of rovibrational lines reaches 32000 per one wavenumberAverage density of rovibrational lines reaches 32000 per one wavenumber..

Salient features of variational anharmonic calculations for the water dimer

A. Pavlyuchko and A. Vigasin, 2008, to be published

Variational anharmonic calculations of the far IR water dimer spectrum

CKD

Water dimer

End-over-endrotation

Intermolecular fundamentals

Intermolecular overtones and combination bands

A. Pavlyuchko and A. Vigasin, 2008, to be published

(Kp = 0.04 atm-1)

Temperature dependence of the continuum binary absorption coefficient

Spectral variations of the metastable (monomer) and stable dimer

absorption cross-sections

Metastable dimers(monomers)

True dimers

Gibbs free energy of dimerization

1.1. The involvement of different types of pair states in the water The involvement of different types of pair states in the water vapor continuum absorption is essentially subject to vapor continuum absorption is essentially subject to temperature.temperature.

2.2. In the vicinity of room temperature these are true bound and In the vicinity of room temperature these are true bound and metastable dimer states which are likely to dominate the metastable dimer states which are likely to dominate the continuum.continuum.

3.3. To all appearance there is no room to speculations about so-To all appearance there is no room to speculations about so-called collision-induced nature of the atmospheric continuum called collision-induced nature of the atmospheric continuum implying that this phenomenon might be determined by free implying that this phenomenon might be determined by free collisional pair states.collisional pair states.

Monomer far wings or water dimers?

• Pair states in the atmosphere realize in terms of true bound, metastable, and free states

• Close collisions may give rise to increase in continuum absorption at elevated temperature

• Involvement of the metastable states is largely responsible for the observed spectral variations in the temperature dependence of the water vapor continuum absorption

Conclusions

Acknowledgments

Yuri I. Baranov, ObninskObninsk

Beatrice Bussery-Honvault, BesanBesanççonon

Sergey V. Ivanov, TroitskTroitsk

Sergey E. Lokshtanov, MoscowMoscow

Anatoly I. Pavlyuchko, VolgogradVolgogradRFBR Grant 08-05-

00140

My thanks go to

The organizers of the current CAVIAR meeting

and to

The audience for your attention