HD+ Photodissociation in an Ultrashort Infrared Laser

Pulse: Carrier-Envelope Phase Difference Effects

Vladimir Roudnev and

B.D. Esry

The work is supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, Us. Department of

Energy, and by the Research Corp.

Motivation

Could any asymmetry be observed in HD+

photodissociation?

How to treat dissociation processes in the presence of ionization?

What kind of asymmetries might be expected?

Topics

3D model (1 nuclear+2 electron degrees of freedom) of the HD+ ion in a laser field

Numerical solution of the time-dependent Schroedinger equation (TDSE)

The HD+ ion in the field of intense (4× to 9×1014W/cm2) 10fs linearly polarized 790 nm laser pulse: calculation results

Carrier-envelope phase effects observability for reaction probabilities

Fragments' velocity distribution in scaled coordinate approach

Carrier-envelope phase effects observability for fragments' velocity distributions

Coordinate system for HD+ molecule

xe

ye

E

Intrinsic coordinates:

Time-dependent Schroedinger equation

The time evolution

• Operator splitting

● Cayley approximant

Single and double-scale approximants

Partial approximants

Double-scale approximant

Single-scale approximant

Ionization probabilities intensity dependence

Channel separation: domains in the configuration space

Different channels can be identified by the corresponding domains in the configuration space

z

R

H+d

p+D

M

Electron density distribution

z (a.u.)

t (a.u.)

I=8 1014 W/cm2

CEPD=π

H+d channel dominates

I=8 1014 W/cm2

CEPD=0

D+p channel dominatesz (a.u.)

t (a.u.)

Dissociation probabilities phase dependence

Laser phase averaged dissociation probabilities

Orientation averaged dissociation probabilities

I=6×1014 W/cm2 I=7×1014 W/cm2

I=8×1014 W/cm2 I=9×1014 W/cm2

The dissociation asymmetry observability

●Controlled carrier-envelope phase difference

●Oriented molecules

●Controlled carrier-envelope phase difference

●Not oriented molecules

●Uncontrolled carrier-envelope phase difference

Channel asymmetry is revealed in total dissociation

Channel asymmetry is revealed in spatial distribution of dissociated fragments

No channel asymmetry is expected

Scaled coordinates approach

Scaled coordinate approach: properties

– Bound states shrink with time

– Continuum states approach a stationary distribution at large times

– Momentum distribution of the continuum part can be obtained from the asymptotic stationary state by simple rescaling

– Continuum states converge to the rescaled momentum distribution faster than O(R(t)-3/2)

Rescaling:

Scaled coordinates distribution converges to momentum distribution

Free particle Bound state in a laser field

t=2500

t=1500

t=3500

t=0

t=5

t=10

Fragment velocity distribution CEPD variation

D velocity (au)H velocity (au)

CE

PD

/π

Orientation averaged fragment velocity distribution

CEPD variation

D velocity (au)H velocity (au)

CE

PD

/π

CEPD effects for the fragments of fixed velocity

Summary• Strong CEPD effects are expected for

dissociation of the HD+ molecule in 10 fs 785 nm laser pulse

• Reaction asymmetries can be observed only if the laser CEPD is controlled, charged and neutral reaction fragments must be registered separately

• The effect is much stronger if fragment velocity selection is performed

Future

• What are the velocity distributions for ionization?

• How the initial state affects the results?

• How to improve the accuracy/perfomance?