1. Isomeric effects on fragmentations of crotonaldehyde and methacrolein in low energy electron–molecule collisions
Arup K. Ghosh, Aparajeo Chattopadhyay and Tapas Chakraborty
Physical Chemistry Department
Indian Association for the Cultivation of Science
Jadavpur, Kolkata , India
69th International Symposium on Molecular Spectroscopy
17th June, 2014

2. (methacryloyl peroxy nitrate)
Aim of the study hν
313 nm >  > 200 nm CO
CH4 ● H●
HCO●
Crotonaldehyde
Isoprene
OH/O2
NO/O2
Cigarette Smoke
Biogenic Emission
from forests
Wheat Straw
Solar UV radiation produce photoelectrons in the atmosphere. Primary auroral electrons ionize the atmospheric gases producing secondary electrons. β α UV
radiation
OH/O3/NOx e-
OH/O2
NO2/O2
PAN
(methacryloyl peroxy nitrate)
OOH 
Hydroxyacetone
VOCs
Methacrolein β α
E. R. Allen, J. N. Pitts Jr., J. Am. Chem. Soc., 91, 3135, 1969.
Physics and chemistry of the upper atmosphere, M. H. Rees, 1989.
Volatile Organic Compounds in the Atmosphere, R. Koppmann, 2007.
J.D. Crounse, H. C. Knap, K. B. Ørnsø, S. Jørgensen, F. Paulot, H.G. Kjaergaard, P.O. Wennberg, J. Phys. Chem. A, 116, 5756, 2012.

3. Reaction Scheme and Product Analysis
Reaction Zone
Analysis Zone
Channeltron
detector
- -5 kV
-2 kV e
Quadrupole mass analyzer
Electron Gun
Sample
Turbo pump
Diffusion pump
Signal
Computer
Sample Inlet

4. Products formed after collisions with electrons having kinetic energy of 12 eV
Crotonaldehyde
(I.E. = 9.73 eV)
Methacrolein
(I.E. =9.92 eV)
CO loss channel
CO loss channel
Molecular ion
Molecular ion
HCO loss channel
HCO loss channel
H loss channel
H loss channel + ● + ● ●+ ●+ + 70 + + 42 70 30 40 50 60 70
m/z + 41 42 69
CH3CO+ 41 69
12 eV 30 40 50 60 70
m/z
A. K. Ghosh, A. Chattopadhyay, A. Mukhopadhyay, T. Chakraborty, Chem. Phy. Lett., , 24-30, 2013.

5. A comparison of the dissociation channels…
Crotonaldehyde
Methacrolein ●+ ●+ + ● + ● 10 eV + + +
CH3CO+
10 eV + 12 eV
12 eV 15 eV 30 40 50 60 70
m/z
15 eV 30 40 50 60 70
m/z

6. Variation of ion yield with the kinetic energy of electrons:
e-KE (eV)
Intensity (arb. units)
Molecular
Ion
H loss
channel + ●+
Intensity (arb. units)
e-KE (eV)
CO loss
channel
HCO loss + ● +

7. Transition states for the H loss channels:
e-KE (eV)
Intensity (arb. units) +
2.027
1.418
1.347
1.123
1.401
1.354
1.02 eV
1.461
1.352
1.113
Methacrolein ion
1.13 eV
1.964
1.136
1.393
1.359
1.419
1.365
1.112
1.126
1.378
1.366
1.06 eV
0.94 eV
Crotonaldehyde ion
Energy
(eV)
DFT/B3LYP/ G(d,p)
Reaction co-ordinate

8. Transition states for the CO loss channels:+ ●
Intensity (arb. units)
e-KE (eV)
2.007
2.524
1.097
1.47 eV
1.461
1.113
1.092
-0.1 eV
Methacrolein ion
1.103
2.493
1.971
1.419
1.112
1.089
0.13 eV
Crotonaldehyde ion
Energy
(eV)
1.98 eV
DFT/B3LYP/ G(d,p)
Reaction co-ordinate

9. The HCO loss channel of crotonaldehyde and methacrolein cations:+
Intensity (arb. units)
e-KE (eV) +
Relative Energy (eV) C1 C2 C3 C4
Crotonaldehyde cation C1 C2 C3 C4
Methacrolein cation
C1-C2 Bond Length (Å)
DFT/B3LYP/ G(d,p)

10. The acetyl cation (CH3CO+) at m/z 43
1.166
1.310
1.518
1.534
EK (0.17)
1.376
1.133
1.493
DMK (0.15)
1.372
1.483
1.558
EK + (8.92)
1.131
1.311
1.169
1.514
DMK + (8.63)
Relative Energy (eV)
1.223
1..537
1.460
1.340
MVK+ (9.43)
Ionization
1.233
1.419
1.365
1.470
CA+ (9.49) Ha
1.217
1.461
1.504
1.352
MA+ (9.68)
1.213
1.467
CA (0.0)
1.211
1.484
1.501
1.339
MA (0.03)
We suggest that MA+ undergoes isomerization to form methyl vinyl cation (MVK+) and dissociation of MVK+ produces the acetyl cation.

11. Summary:
The two isomeric compounds studied here show similar fragmentation channels, however, the relative yields of the fragmentation are different.
The differences in product yields can be explained qualitatively from their relative stabilities.
Electronic structure calculation predicts similar trends, and the transition states being structurally similar to the products, the relative TS energies correspond to the product stabilities.

12. Acknowledgements: All my labmates Funding:
Council of Scientific and Industrial Research (CSIR), India

13. THANK YOU