The Thexi State

1. The State of Thermal
Excitation- “THE
THEXI STATE”
By:- Harsh Jaswal
Student of:- Central University of Himachal
Pradesh
Roll no.:- CUHP19CCSO9
Department :- Department of Chemistry and

2. What is “State”?
֍In chemistry the State is the set of
combination of the electronic, chemical and
physical properties of the atom.
֍For example, Oxidation state is the
number of electrons that an atom can gains
or losses in order to form a chemical bond.
֍We will restrict our discussion on
electronic states. i.e., Ground state and
Excited state only.
֍Ground states and Excited states may
considered isomer (nuclear isomer) to one
another as they have same atomic number

4. Ground State (GS)Vs. Excited
State(ES)
֍GS is the state in
which all electrons in
a system are in the
lowest possible
energy level.
֍Also called as
“ZERO” energy.
֍Highly stable.
֍Has long lifetime.
֍Distance between
the electron and
nucleus is least.
֍ES is any state of
the system that has
a higher energy than
the GS.
֍Has higher energy.
֍Highly Unstable.
֍Has short lifetime.
֍Has more distance
between the electron
and nucleus.

5. How to Excite an electron?
֍2 ways to excite the electrons are
(1) By Absorption of energy &
(2) By Collisions (inelastic).

6. Excitation by absorption of
energy
Excitation
Processes
Thermal
Excitation
Electronic
Excitation

7. Thermal Excited State or “THE
THEXI STATE”
֍T.J Meyer and his coworkers proposed
that we can use the term “THEXI STATE”
for Thermal Excited State.

8. ֍Properties of Thexi States are
independent of how they are prepared.
֍Chemically, Thexi state is an isomer of
the ground state.
֍Thexi state is good thermodynamic and
kinetic specie.
֍It is very difficult to determine spin
multiplicity and actual structure of Thexi
state specie.

9. Properties of Thexi State
A. Preparation:-
Excited states do not last very long. They
only lasts for few milliseconds (ms) range in
room temperature solution. As a
consequence, they must be prepared in
situ.
One of the simplest way of preparing Thexi
State is by method of irradiation or energy
transfer, Photo excitation, by shock wave of
laser.

10. Light is absorb by photosensitizer
molecule S, to form S* which then transfer
energy to A, which then forms A* and S.
Example:-
bpy= 2,2-bipyridine
2 3 * 3 * 2
3 3 3 3
( ) [ ( ) ] [ ( ) ] ( )
Cr bpy Ru bpy Cr bpy Ru bpy
   
  
* *
A S A S
  

11. B. Emission:-
Thexi state will return to ground state with
emission of radiation/energy/light.
The emission yield is determine by:-
is emission yield
is yield of A*
is constant of proportionality
reciprocal of emission lifetime
* ( / )
e A r e
k k
 

e

*
A

e
k
r
k

12. Why to study the emission?
The Thexi state, spectra help us in
determining the excited state of the
reaction.
Like in the reaction,
Due to the emission spectra we came to
know that the excited state in the product
is that of Cr and not of Ru.
2 3 * 3 * 2
3 3 3 3
( ) [ ( ) ] [ ( ) ] ( )
Cr bpy Ru bpy Cr bpy Ru bpy
   
  

13. C. Energy:-
The thermal equilibration process not only
involves geometry changes, but also a loss
in energy.
Zero-Zero transition means transitions from
the zero vibrational level of the ground state
to the zero vibrational level of the excited
state. Which is very difficult to determine.
The region of overlap of absorption and
emission spectra gives an account of the
Thexi State Energy.

14. D. Spectroscopy:-
The excited state absorption (ESA) is still
very uncommon. One may uses a light
source beam at right angles to the laser
pulse that generates A*, and measures the
attenuation of the beam.
ESA has been absorbed for:-
spectra at 370nm and 520nm,
show ESA at 490nm
and 620nm.
No infrared ESA (ESIR) has been reported
yet.
3 5 4
( ) ( )
Cr NH NCS 
2 2
3 5 3 5
.[ ( ) ] & [ ( ) ]
aq Rh NH Cl Rh NH Br
 

15. E. Rate Processes:-
For Thexi State, we have two types of rate
processes:-
Intersystem Crossing and Internal
Conversion.
Change in Composition or charge.
K is rate constant, r is average distance of
reactants, D is diffusion coefficient, N0 is
Avogadro number, t is temperature and is
electrostatic attraction.
/
4
1000
t
o
d
rDN
k e 





17. F. Structure:-
It is very difficult to determine actual
structure of Thexi state specie.

18. Thank
you