1. Infrared Spectroscopy of CH2Cl in Solid Parahydrogen
Yuki Miyamoto and Takamasa Momose
University of British Columbia T

2. CH2Cl (Chloromethyl Radical)
An important radical in atmospheric/environmental chemistry
Source of Chlorine atom
Ozone destroyer
Spectroscopic studies
Matrix isolation
Jacox and Milligan, J. Chem. Phys. 53, 2688 (1970).
Andrews and Smith, J. Chem. Phys. 53, 2956 (1970).
High resolution in gas phase
MW: Endo et al. Can. J. Phys. 62, 1347 (1984).
MW: Bailleux et al. J. Mol. Spectrosc. 229, 140. (2005)
IR: Whitney et al. J. Chem. Phys. 125, (2006).
A planar structure (C2v) with the ground electronic state of 2B1

3. CH2Cl (Chloromethyl Radical)
a source of 1CH2 and 3CH2
Dribinski et al. J. Chem. Phys. 115, 7474 (2001).
CH2Cl + UV ( nm) → CH2 (a1A1) + Cl (2P3/2,1/2)
CH2Cl + UV ( nm) → CH2 (X3B1) + Cl (2P1/2)

4. Parahydrogen Matrix 1) Quantized rotation of small dopants
2) Small intermolecular interaction
CD4 / p-H2
0.007 cm-1 = 200 MHz
hexagonal close packed structure
3) Small “cage effect” in situ photolysis
in solid Ne
in solid p-H2

5. Radicals in Parahydrogen Matrix
1. Methyl radical (CH3, CD3)
J. Chem. Phys. 103, 1400 (1995); 108, 7334 (1998);
2. Ethyl radical (C2H5)
J. Phys. Chem. A101, 522 (1997).
3. Carbon chain Cn (n=3, 5, 7, ...)
J. Phys. Chem. 100, (1996).

6. Experiments in situ photolysis of CH2ClI in solid parahydrogen
Senapatiet al. J. Phys. Chem. A106, 8479 (2002).
CH2ClI + UV (>310 nm) → CH2Cl + I
Xe lamp with a UVD36A filter
( nm)
n-s*(C-I)
CH2Cl + UV ( nm)
→ CH2 (a1A1) + Cl (2P3/2,1/2)
CH2Cl + UV ( nm)
→ CH2 (X3B1) + Cl (2P1/2)
1CH2
3CH2

7. Experiments ortho concentration <0.05% sample concentration
< 10 ppm
temperature 3.5 K

8. Photolysis of CH2ClI before UV after UV after annealing
The photolysis occurs efficiently
no other products
CH2ClI + UV (>310 nm) → CH2Cl + I
CH2, CH3, CH4, CH2I etc.

9. Assignments ν2 (CH2 scissors) ν1 (CH2 symmetric-stretch)
ν3 (CCl stretch)
unstable form of CH2Cl ?
after UV
CH2Cl
after annealing
(5K, 5 min)
after 10 h
after 24 h

10. Nuclear Spin Conversion of CH2Cl
CH2Cl has ortho-para spin modifications A B C
Ka = 0, I = 1 ortho
electronic state of 2B1
Ka = 1, I = 0 para
37Cl : 35Cl ~ 1 : 3
37CH2Cl
35CH2Cl
conversion rate
k = K
CH4 I=1(J=1)  I=2 (J=0)
k(CH4) = K
J.Chem. Phys. 128, (2008)
after annealing
after 10 h
after 24 h
Ka = 0, I = 1
Ka = 1, I = 0

11. Rotational Structure 35 37
CH2 sym.-stretch (a1) A-type transition (Ka = 0)
Uniaxial rotation
J’ = 2 1 b
In gas
In p-H2 c
J = 1 a
Ka =
Ka =
Hrot= AJa2+BJb2 +CJc2
Hrot= A Ja2
B,C → 0
35
P,Q,R branches
no P,R branches
37
35Cl Ka = 1
 = A’ – A”
35Cl Ka = 0
p-H2
gas
37Cl Ka = 0
35 
37Cl Ka = 1
0.22 cm-1
0.11 cm-1
37 
0.19 cm-1
0.14 cm-1

12. Concentrated Samples 10 ppm 100 ppm ka=1 ka=0 t = 0 t = 0 t = 10 h
slower nuclear spin conversion
decay of the radicals over a few days

13. Conclusions
The CH2Cl radical was successfully produced by the in-situ photolysis of CH2ClI.
Nuclear spin conversion of CH2Cl was observed.
In a concentrated sample (100 ppm), the nuclear spin conversion was almost suppressed.
The CH2Cl radical probably exhibits uni-axial rotation in the matrix.