Supplementary Materials Figure S1: Effect of cone voltage on positive mass spectra of [BuMeIm][Tf2N]: (a) 10V, (b) 20V, (c) 30V, (d) 40V, (e) 50V, (f) 60V. Figure S2: Effect of cone voltage on negative mass spectra of [BuMeIm][Tf2N]: (a) 10V, (b) 20V, (c) 30V, (d) 40V, (e) 50V, (f) 60V. Figure S3: (a) BuMeIm+ concentration before and after 2.0 MGy radiolysis determined by HPLC and (b) Tf2N- concentrations before and after 2.0 MGy radiolysis determined by 19F NMR in "dry" [BuMeIm][Tf2N], ½ w pre-eq [BuMeIm][Tf2N] and w pre-eq [BuMeIm][Tf2N]. Figure S4: Evolution of X- (X- : Tf2N-, TfO-, PF6

- and BF4-) concentration as a function of the

irradiation dose for [BuMeIm][Tf2N], [BuMeIm][TfO], [BuMeIm][PF6] and [BuMeIm][BF4]. Figure S5: Positive ESI-MS spectra of (a) [BuMeIm][Tf2N], (b) [BuMeIm][TfO], (c) [BuMeIm][PF6] and (d) [BuMeIm][BF4] before radiolysis. Figure S6: Positive ESI-MS spectra of (a) [BuMeIm][Tf2N], (b) [BuMeIm][TfO], (c) [BuMeIm][PF6] and (d) [BuMeIm][BF4] after 2.0 MGy radiolysis. Figure S7: MS/MS spectrum of ion at m/z 207.1. Figure S8: MS/MS spectrum of ion at m/z 157.1. Figure S9: MS/MS spectrum of ion at m/z 556.1. Figure S10: Positive ESI-MS spectra of (a) "dry" [BuMeIm][Tf2N], (b) ½ w. pre-eq [BuMeIm][Tf2N] and (c) w. pre-eq [BuMeIm][Tf2N] after 2.0 MGy radiolysis. Figure S11: (a) UV spectra of [BuMeIm][Tf2N] before and after 2.0 MGy radiolysis (b) Evolution of 290 nm light absorbance as a function of the irradiation dose for irradiated [BuMeIm][Tf2N]. Figure S12: HPLC chromatograms of (a) [BuMeIm][Tf2N] after 2.0 MGy radiolysis at 210 nm and 290 nm light absorbance (b) [BuMeIm][TfO] after 2.0 MGy radiolysis at 210 nm and 290 nm light absorbance, (c) [BuMeIm][PF6] after 2.0 MGy radiolysis at 210 nm and 290 nm light absorbance and (d) [BuMeIm][BF4] after 2.0 MGy radiolysis at 210 nm and 290 nm light absorbance. Figure S13: Total ion current gas chromatogram between 8.0 to 18.0 minutes of (a) [BuMeIm][Tf2N], (b) [BuMeIm][TfO], (c) [BuMeIm][PF6], (d) [BuMeIm][BF4] after 50 kGy radiolysis on Rt-MSieve/Rt-Q PLOT columns.

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m/z100 200 300 400 500 600 700 800 900 1000

%

0

100

%

0

100

%

0

100

%

0

100

%

0

100

%

0

100 139.1558.1

139.9

139.1558.1140.1

139.1558.1140.1

139.1558.1140.1 325.9

139.1140.1 558.1325.8 501.3

139.1140.1 558.1501.3325.9211.2 447.2 621.3679.4

(a)

(b)

(c)

(d)

(e)

(f)

Figure S1: Effect of cone voltage on positive mass spectra of [BuMeIm][Tf2N]: (a) 10V, (b) 20V, (c) 30V, (d) 40V, (e) 50V,

(f) 60V.

m/z100 200 300 400 500 600 700 800 900 1000

%

0

100

%

0

100

%

0

100

%

0

100

%

0

100

%

0

100279.6

280.0698.3

279.6280.1

698.3

279.6281.6

279.6

210.7 281.6

279.6210.7

146.7 282.0

279.6210.7

146.7 281.6

(a)

(b)

(c)

(d)

(e)

(f)

Figure S2: Effect of cone voltage on negative mass spectra of [BuMeIm][Tf2N]: (a) 10V, (b) 20V, (c) 30V, (d) 40V, (e) 50V,

(f) 60V.

Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2009

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

dry 1/2 w-pre-eq w-pre-eq

[Tf 2

N]- (m

ol.L

-1)

Before RadiolysisAfter 2,0 MGy Radiolysis

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

dry 1/2 w pre-eq w pre-eq

[BuM

eIm

]+ (mol

.L-1

)Before RadiolysisAfter 2,0 MGy Radiolysis

(a) (b)

Figure S3 : (a) BuMeIm+ concentration before and after 2.0 MGy radiolysis determined by HPLC and (b) Tf2N-

concentrations before and after 2.0 MGy radiolysis determined by 19F NMR in "dry" [BuMeIm][Tf2N], ½ w pre-eq [BuMeIm][Tf2N] and w pre-eq [BuMeIm][Tf2N].

Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2009

0,0

1,0

2,0

3,0

4,0

5,0

6,0

0 500 1000 1500 2000 2500Dose (kGy)

X- (mol

.L-1

)

Tf2NTfOPF6BF4

Figure S4: Evolution of X- (X- : Tf2N-, TfO-, PF6

- and BF4-) concentration as a function of the irradiation dose for

[BuMeIm][Tf2N], [BuMeIm][TfO], [BuMeIm][PF6] and [BuMeIm][BF4].

m/z100 200 300 400 500 600 700 800 900 1000

%

0

100

%

0

100

%

0

100

%

0

100 139.1558.1

140.1

139.1427.1140.1 429.2

139.1423.1

140.1 424.1

139.1

365.2139.9

(a)

(b)

(c)

(d)

Figure S5: Positive ESI-MS spectra of (a) [BuMeIm][Tf2N], (b) [BuMeIm][TfO], (c) [BuMeIm][PF6] and (d) [BuMeIm][BF4] before radiolysis.

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m/z100 200 300 400 500 600 700 800 900 1000

%

0

100 139.1

558.1

139.4140.1

207.1

559.1560.1

561.1

BuMeImTf2N - irradie

m/z60 80 100 120

%

0

100137.1

125.1119.063.1 119.083.1 103.0

BuMeImTf2N - irradie

m/z150 175 200 225 250 275 300

%

0

100 207.1

201.1157.1

182.1 239.1286.1

BuMeImTf2N - irradie

m/z555 556 557 558 559

%

0

100 558.1

556.1

(a)

m/z100 200 300 400 500 600 700 800 900 1000

%

0

100 139.1

427.1

140.1

207.1428.1

BumimTfO irr - ESP+

m/z60 80 100 120

%

0

100137.1

125.1115.165.5 74.1 102.6

BumimTfO irr - ESP+

m/z424 425 426 427 428

%

0

100 427.1

BumimTfO irr - ESP+

m/z150 175 200 225 250 275 300

%

0

100 207.1

153.1 194.9

157.1181.1

252.2

210.1224.2 253.2

293.2

(b)

Electronic Supplementary Information for Dalton TransactionsThis journal is © The Royal Society of Chemistry 2009

m/z100 200 300 400 500 600 700 800 900 1000

%

0

100 139.1

423.2

140.1

424.2

BuMeImPF6-2MGy

m/z60 80 100 120

%0

100137.1

123.0122.195.383.170.665.0

BuMeImPF6-2MGy

m/z150 175 200 225 250 275 300

%

0

100 157.1

266.2167.1 195.2 224.2 284.3

BuMeImPF6-2MGy

m/z420 421 422 423 424

%

0

100 423.2

421.2

(c)

m/z100 200 300 400 500 600 700 800 900 1000

%

0

100 139.1

365.2140.1

157.1 364.2366.2

BuMeImBF4-2MGy

m/z60 80 100 120

%

0

100137.1

118.0

69.556.7 92.576.8 116.0

120.0

136.0

BuMeImBF4-2MGy

m/z150 175 200 225 250 275 300

%

0

100 157.1

224.2182.2

158.1 210.1 252.2293.2277.2

BuMeImBF4-2MGy

m/z362 363 364 365 366

%

0

100 365.2

364.2

363.2 365.5

(d)

Figure S6: Positive ESI-MS spectra of (a) [BuMeIm][Tf2N], (b) [BuMeIm][TfO], (c) [BuMeIm][PF6] and (d) [BuMeIm][BF4] after 2.0 MGy radiolysis.

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60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250m /z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rel

ativ

e A

bund

ance

151.1

83.1

207.3187.2178.7 192.1165.0 199.5138.9 150.1 152.5124.2 134.1 222.7207.882.0 95.5 238.7234.8108.9 245.2120.972.3

- C5H7F3

- C4H8

Figure S7: MS/MS spectrum of ion at m/z 207.1.

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60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250m /z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100R

elat

ive

Abu

ndan

ce137.1

83.1

101.1

128.995.1 118.5115.9 176.355.6 142.1 189.374.3 206.2151.2 217.3157.386.070.0

- C4H7F

- C4H8

- HF

Figure S8: MS/MS spectrum of ion at m/z 157.1.

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091008-02 #1-44 RT: 0.04-1.99 AV: 44 NL: 4.09E3T: + p ESI Full m s2 556.00@40.00 [ 150.00-1000.00]

200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000m /z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rel

ativ

e A

bund

ance

275.2

193.2

219.2

261.3163.1 474.0

538.0500.1 556.5259.3 431.4404.1352.9290.0 901.3714.4

-C4H6N2

-HTf2N

-C4H8

Figure S9: MS/MS spectrum of ion at m/z 556.1.

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Tf2N

m/z50 100 150 200 250 300 350 400 450 500 550 600

%

0

100

%

0

100

%

0

100

GL240209-10 95 (2.115) TOF MS ES+ 9.26e3x6 139.6

137.6

140.6558.3

207.6181.6 556.3420.3242.7 334.4

559.3

GL240209-12 108 (2.405) TOF MS ES+ 1.26e4x6 139.6

137.6

140.6558.3

207.6181.6 556.3334.4286.5 420.3 559.3

GL240209-14 5 (0.118) TOF MS ES+ 1.26e4x6 139.6

137.6

140.6558.3

207.6181.6 326.3286.5 556.3363.6 420.3 559.4

(a)

(b)

(c)

Figure S10: Positive ESI-MS spectra of (a) "dry" [BuMeIm][Tf2N], (b) ½ w. pre-eq [BuMeIm][Tf2N] and (c) w. pre-eq [BuMeIm][Tf2N] after 2.0 MGy radiolysis.

After Radiolysis

Before Radiolysis

(a)

(b)

0.00.51.01.52.02.53.03.54.04.55.0

200 250 300 350 400 450 500nm

Abs

orba

nce

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 500000 1000000 1500000 2000000Dose (Gy)

Abs

orba

nce

Figure S11: (a) UV spectra of [BuMeIm][Tf2N] before and after 2.0 MGy radiolysis (b) Evolution of 290 nm light

absorbance as a function of the irradiation dose for irradiated [BuMeIm][Tf2N].

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Time (min) Time (min)

Are

a (m

Au)

Are

a (m

Au)

0

5000

10000

15000

20000

25000

8 13 18 23 28 33 38

210 nm290 nm

0

5000

10000

15000

20000

25000

8 13 18 23 28 33 38

210 nm290 nm

Time (min) Time (min)

(a) (b)

Are

a (m

Au)

Are

a (m

Au)

0

5000

10000

15000

20000

25000

8 13 18 23 28 33 38

210 nm290 nm

0

5000

10000

15000

20000

25000

8 13 18 23 28 33 38

210 nm290 nm(c) (d)

Figure S12: HPLC chromatograms of (a) [BuMeIm][Tf2N] after 2.0 MGy radiolysis at 210 nm and 290 nm light absorbance

(b) [BuMeIm][TfO] after 2.0 MGy radiolysis at 210 nm and 290 nm light absorbance, (c) [BuMeIm][PF6] after 2.0 MGy radiolysis at 210 nm and 290 nm light absorbance and (d) [BuMeIm][BF4] after 2.0 MGy radiolysis at 210 nm and 290 nm

light absorbance.

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2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00

400006000080000

100000120000

Abu

ndan

ce

Time (min)

Abu

ndan

ceA

bund

ance

Abu

ndan

ce(a)

(b)

(c)

(d)

C4H8

C3H6

C3H8C3H7F

C4H10

C4H8

C4H7OH

C2H6

C2H4

Figure S13: Total ion current gas chromatogram between 8.0 to 18.0 minutes of (a) [BuMeIm][Tf2N], (b) [BuMeIm][TfO], (c) [BuMeIm][PF6], (d) [BuMeIm][BF4] after 50 kGy radiolysis on Rt-MSieve/Rt-Q PLOT columns.

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