Absolute Photoionization Cross-Section of the Vinyl Radical
Supporting Information
John D. Savee,1 Jessica F. Lockyear,2 Sampada Borkar,3 Arkke J. Eskola,1 Oliver Welz,1 Craig
A. Taatjes,1 and David L. Osborn1,a)
1
Combustion Research Facility, Mail Stop 9055, Sandia National Laboratories, Livermore, CA
94551-0969 USA
2
Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 USA
3
Department of Chemistry, University of the Pacific, Stockton, CA 95211 USA
Contents:
1. Absolute cross-section measurements using photoionization mass spectrometry
2. Absolute cross-section measurements from methyl vinyl ketone
3. Absolute cross-section measurements from vinyl iodide
4. Adiabatic ionization energy of the vinyl radical
a)
Corresponding authors: jdsavee@sandia.gov, dlosbor@sandia.gov
1
1. Absolute cross-section measurements using photoionization mass spectrometry
As described by Cool et al.,1 the relationship expressed in Eq. S1 can be made between
the observed signal for two different species (denoted i and j) in photoionization mass
spectrometry experiments.
 Si ( E )   N j    j 


 S ( E )   N    
 j
  i  i
 i (E)   j (E)  
(S1)
Here,  represents the photoionization cross-section, E is the photoionization energy, S is the
observed signal, N is the concentration, and  is the instrumental mass discrimination factor,
which accounts for mass-dependent sampling efficiencies. In this manner, the photoionization
cross-section for an unknown species (i) can be obtained relative to the known cross-section for
another species (i.e., j). The present experiments exploit time-resolved signal from flash
photolysis in a slow-flow reactor, which is coupled to a multiplexed photoionization mass
spectrometer,2 to evaluate signal ratios (Si/Sj) via kinetic modeling and extrapolation to the signal
levels immediately following photolysis (see equation S2 below). The instrumental mass
discrimination (i, j) can be readily measured at a given temperature and pressure,3 and for
these experiments it can be parameterized as (m/z)(0.643  0.086). Although it can be straightforward
to measure concentration ratios of stable species (Ni/Nj), this term becomes difficult to quantify
when working with transient products such as highly reactive free-radicals. Similar to the
methods developed by Flesch4 and Neumark,5 the present experiments determine the absolute
photoionization cross-section of the vinyl radical by exploiting chemical systems in which
photolysis creates products with a known or easily determined Nj/Ni ratio as discussed below.
2
2. Absolute cross-section measurements from methyl vinyl ketone photolysis
Fahr et al. have studied the 193 nm photolysis of methyl vinyl ketone (MVK,
CH3C(O)C2H3) and report a value of Nmethyl/Nvinyl = (1.11  0.04) at low pressure ( 100 - 300
Torr) and room temperature.6 This ratio of the methyl and vinyl radical yield exhibited no
significant change over this range of pressures, and we assume that the reported value will also
be accurate at the 4 Torr and 298 K conditions of the present experiments.
A photoionization spectrum between 8.124 and 11.024 eV ( 30 meV resolution) of the
products resulting from 193 nm photolysis of a gas flow containing 1.6  1013 cm-3 MVK seeded
in excess helium was obtained to aid confirmation that m/z = 15 and m/z = 27 products were due
solely to methyl and vinyl radicals, respectively. The resulting photoionization spectrum
observed at m/z = 15 is shown in Fig. S1 and is confirmed to arise from ionization of the methyl
radical and not from dissociative ionization of a higher mass species based on the similarity of
the measured spectrum to that of the methyl radical.7 The simultaneously acquired signal of
C2H3+ detected at m/z = 27 is shown in Fig. 1 in the main text. The sharp autoionizing features
observed in the m/z = 27 photoionization spectrum obtained by Berkowitz et al. from the F +
C2H4 reaction are also apparent in our spectra, although there are intensity differences between
the two spectra above  10.2 eV (see main text for more discussion).8 We conclude that the m/z =
27 spectrum from 193 nm photolysis of MVK arises solely from the vinyl radical due its
similarity to the spectrum obtained from 248 nm photolysis of vinyl iodide (Fig. 1 of the main
text).
3
Single energy determinations of the absolute photoionization cross-section of the vinyl
radical at 10.224 and 10.424 eV ( 30 meV resolution) were carried out using 193 nm photolysis
of a flow containing [MVK]0 = 5.2  1012 cm-3 seeded in helium at 4 Torr and 298 K. Lower
concentrations of MVK (relative to that used for photoionization scans) were used for these
measurements to ensure radical concentrations were small enough to obtain accurate signal
determinations from fits to a kinetic model (see below). With a laser fluence of  35 mJ/cm2 at
193 nm, 47% of the MVK was depleted upon photolysis resulting in total initial radical
concentrations of  4.9  1012 cm-3. The observed time profiles for methyl (m/z = 15.023) and
vinyl (m/z = 27.023) at both 10.224 and 10.424 eV are shown in Fig. S2. A fit of these time
profiles to a combined first- and second-order kinetic decay function (Eq. S2) convolved with the
temporal instrument response was used to determine Smethyl and Svinyl immediately following
photolysis3,9 (also shown in Fig. S2), and the results of the fit are presented in Table S1.
Si (t ) 
Si (t  0)  k1
(2k   k1 )e k1 t  2k 
(S2)
Here Si(t) is the observed signal for species i, t is the time after photolysis, k1 is a first-order rate
constant representing the sum of all first-order removal processes including heterogeneous wall
loss, and k=k2[i]t=0, where k2 is the second-order rate constant describing total second-order
losses of species i. Equation S2 gives a good fit to the measured time profiles and should
therefore provide an accurate extrapolation of the signal intensities immediately following
photolysis. Because a full kinetic description of the transient time profiles of CH3 and C2H3 was
not the goal of this study and because there might be a strong correlation between k1 and k, we
only use these fits for extrapolation purposes, not to infer kinetic information from the obtained
values for k1 and k.
4
In order to fully quantify Eq. S1 to obtain vinyl at 10.224 and 10.424 eV, methyl must also
be known at these photon energies. The high signal-to-noise absolute photoionization crosssection spectrum presented in Ref.
3
can be linearly interpolated to yield methyl(10.224 eV) =
(5.3  1.1) Mb (1 Mb = 10-18 cm2) and methyl(10.424 eV) = (5.8  1.2) Mb. The reported error
assumes a  20% uncertainty in the interpolated value of the photoionization cross-section. With
these results, Eq. S1 can be used to establish values of vinyl(10.224 eV) = (6.1  1.4) Mb and
vinyl(10.424 eV) = (8.3  1.9) Mb with errors reported at the 2 level of uncertainty. These
propagated errors are  25% of the nominal value and represent a conservative estimation of the
uncertainty. It should be noted that comparison of vinyl radical signal to the amount of depleted
MVK was considered (similar to the method used with vinyl iodide as discussed below) but not
carried out due to evidence for significant depletion of MVK after photolysis via reaction with
photolytically produced radicals.
3. Absolute cross-section measurements from vinyl iodide photolysis
Photodissociation of vinyl iodide (C2H3I) at 248 nm was used for a second independent
determination of the absolute photoionization cross-section of the vinyl radical relative to the
vinyl iodide precursor. The initial concentration of vinyl radicals relative to vinyl iodide was
obtained from the depletion signal of vinyl iodide. This method relies on the knowledge of the
quantum yield of the vinyl radical from photodissociation. Yamashita et al. found evidence that
at 254 nm vinyl + I-atom was the dominant product channel (quantum yield of  0.85), with the
remainder of the photodissociation of vinyl iodide forming HI + C2H2.10 Zou et al. studied the
photodissociation of vinyl iodide and concluded that the vinyl + I-atom product channel is by far
the dominant dissociation pathway between 193 and 266 nm with a quantum yield of > 0.91.
Furthermore, they found no significant evidence for the competing HI + C2H2 channel.11 In the
5
present study a large spike in the HI signal (and also I-atom signal, see Fig. S3) obscured the
early-time behavior of the otherwise gradual HI production (consistent with secondary and not
direct photolytic production) and prevents any meaningful contributions to this debate. The
magnitude of this spike at early time in the HI and I-atom kinetic profiles exhibits a dependence
on the photolysis laser fluence that is consistent with a multiphoton process, although the exact
origin is not known.
Close examination of the HI signal in the upper panel of Fig. S3 suggests a non-zero
signal value upon linear extrapolation of the data back to the instant following photolysis.
However, the ratio of the HI to I atom signal linearly extrapolated back to the instant following
photolysis suggests an approximately 1:25 signal ratio. Under the assumption that HI and I-atom
have the same photoionization cross-section at 10.5 eV, these observations suggest only a minor
( 4%) direct yield of HI. However, it is possible (and not discernible in the present experiments)
that the fast decaying component of the I-atom signal rapidly gives rise to HI, which would
further reduce the direct photolytic yield indicated by the non-zero signal offset.
Under the assumption that 248 nm photolysis of vinyl iodide produces vinyl + I-atom
with a unity quantum yield, the vinyl radical concentration (Nvinyl) immediately following
photolysis is equal to the concentration of photodissociated vinyl iodide. More concisely stated,
Nvinyl =  S C H I  [C2H3I]0 and N C H I = [C2H3I]0 (1 –  S C H I ) where  S C H I is the fractional
2
3
2
3
2
3
2
3
precursor depletion measured from time-resolved signal in the present experiments and N C H I is
2
3
the concentration of C2H3I after photolysis. The ratio of the two concentrations, N C H I / Nvinyl, is
2
3
equal to (1 -  S C H I ) /  S C H I and is independent of the initial vinyl iodide concentration. If the
2
3
2
3
quantum yield for production of I + vinyl radical at 4 Torr and 298 K is found to be less than
6
unity, the absolute photoionization cross-section derived should be divided by the revised
quantum yield.
The absolute photoionization cross-section of vinyl iodide was measured in a
straightforward manner relative to propene12,13 between 9.1 and 11 eV (reported in Table S2). In
agreement with the observations of Shuman et al., no m/z = 27 (C2H3+) signal from dissociative
ionization of vinyl iodide was observed in this photon energy range.14 Interpolation of this
absolute spectrum yields vinyl iodide cross-section values of 25.9, 50.9, and 53.0 Mb at 10.013,
10.513, and 10.813 eV, respectively (the energies at which vinyl cross-section measurements
were made as described below). Errors in the absolute cross-section values determined here are
expected to be on the order of  20%.
A photoionization spectrum for the m/z = 27 product formed after 248 nm photolysis of
C2H3I at 4 Torr and 298 K in a flow containing [C2H3I]0 = 1.9  1012 cm-3 seeded in excess
helium was also obtained, and is presented in Fig. 1 of the main text. Despite intensity
differences from the vinyl radical spectrum obtained by Berkowitz et al. at photon energies >
10.2 eV,8 the similarity of this spectrum to the m/z = 27 spectrum obtained from photolysis of
MVK strongly suggests that both spectra arise solely from the vinyl radical.
Single energy measurements of the photoionization cross-section were obtained at
10.013, 10.513, and 10.813 eV ( 30 meV resolution) using a flow containing [C2H3I]0 = 1.9 
1012 cm-3 seeded in excess helium. Typical vinyl iodide depletions were SC H I  3.5% and
2
3
assuming a unity quantum yield for production of vinyl + I atoms we estimate initial vinyl
radical number densities of  6.6  1010 cm-3 immediately after photolysis. Due to the
prohibitively high count rate associated with vinyl iodide at m/z = 154,15,16 which leads to
7
saturation of the m/z = 154 signal but does not affect other mass channels, the vinyl iodide signal
was determined using the average signal from 2 to 20 ms after photolysis from the 13C isotopolog
of vinyl iodide at m/z = 155 (see Table S3). Signal immediately following photolysis for the
vinyl radical at m/z = 27 was determined by fitting the transient time profile using Eq. S2; the
results from the fits are also reported in Table S3. The time profiles of m/z = 27 and 155 at the
three photon energies are presented in Fig. S4 along with the fits to the m/z = 27 time profiles.
These results yield absolute cross-section determinations of vinyl(10.013 eV) = (4.7  1.1) Mb,
vinyl(10.513 eV) = (9.0  2.1) Mb, and vinyl(10.813 eV) = (12.1  2.9) Mb.
Using a weighted linear least-squares fit to the absolute vinyl values determined from
both MVK and vinyl iodide photolysis at single photon energies, the sum of the relative vinyl
radical photoionization spectra obtained from photolysis of MVK and vinyl iodide can be placed
on an absolute basis as shown in Fig. 2 of the main text. The absolute photoionization crosssection values of the scaled vinyl radical spectrum are also reported in Table S4. There does
appear to be a steeper slope of cross-section vs. increasing photon energy in our five individual
measurements compared to the relative photoionization spectrum (Fig. 2). The reason for these
different slopes is not obvious, and we feel that without reasons to prefer one determination over
another, a weighted fit of the relative photoionization spectrum to all five absolute cross-section
determinations is the most justifiable approach.
4. Adiabatic ionization energy of the vinyl radical
The adiabatic ionization energy (AIE) of the vinyl radical is a topic of considerable debate.
Experimental and computational determinations range from 8.25 to 8.95 eV, although the most
recent studies have converged on a value of  8.5 eV that results from direct ionization of the
8
neutral ground state to a bridged geometry ground state cation (i.e., X  ( 1 A)  X ( 2 A) ).8,17-21
The Franck-Condon factors governing this transition are expected to be extremely weak near the
ionization threshold due to the large geometry difference between the neutral and cationic states,
as described, e.g., by Berkowitz et al.8 Because of the resulting slow rise of the photoionization
spectrum as a function of photon energy near the ionization threshold and also due to the low
resolution of the present experiments ( 30 meV) we cannot significantly contribute to the debate
over the AIE of the vinyl radical, although the onset of signal in the present experiments
provides an upper limit lying between the values (8.51  0.03) eV evaluated recently by Lago
and Baer18 and (8.59  0.03) eV determined by Berkowitz et al.8
References
(1)
T. A. Cool, A. McIlroy, F. Qi, P. R. Westmoreland, L. Poisson, D. S. Peterka, and M.
Ahmed, Rev. Sci. Instrum. 76, 094102 (2005).
(2)
D. L. Osborn, P. Zou, H. Johnsen, C. C. Hayden, C. A. Taatjes, V. D. Knyazev, S. W.
North, D. S. Peterka, M. Ahmed, and S. R. Leone, Rev. Sci. Instrum. 79, 104103 (2008).
(3)
J. D. Savee, S. Soorkia, O. Welz, T. M. Selby, C. A. Taatjes, and D. L. Osborn, J. Chem.
Phys. 136, 134307 (2012).
(4)
R. Flesch, M. C. Schurmann, J. Plenge, M. Hunnekuhl, H. Meiss, M. Bischof, and E.
Ruhl, Phys. Chem. Chem. Phys. 1, 5423 (1999).
(5)
J. C. Robinson, N. E. Sveum, and D. M. Neumark, J. Chem. Phys. 119, 5311 (2003).
(6)
A. Fahr, W. Braun, and A. H. Laufer, J. Phys. Chem. 97, 1502 (1993).
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J. D. Savee, O. Welz, C. A. Taatjes, and D. L. Osborn, Phys. Chem. Chem. Phys. 14,
10410 (2012).
9
(8)
J. Berkowitz, C. A. Mayhew, and B. Ruscic, J. Chem. Phys. 88, 7396 (1988).
(9)
O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Percival, D. E. Shallcross, and C. A.
Taatjes, Science 335, 204 (2012).
(10)
S. Yamashita, S. Noguchi, and T. Hayakawa, Bull. Chem. Soc. Jpn. 45, 659 (1972).
(11) P. Zou, K. E. Strecker, J. Ramirez-Serrano, L. E. Jusinski, C. A. Taatjes, and D. L.
Osborn, Phys. Chem. Chem. Phys. 10, 713 (2008).
(12) O. Welz, J. Zador, J. D. Savee, M. Y. Ng, G. Meloni, R. X. Fernandes, L. Sheps, B. A.
Simmons, T. S. Lee, D. L. Osborn, and C. A. Taatjes, Phys. Chem. Chem. Phys. 14, 3112
(2012).
(13)
J. C. Person, and P. P. Nicole, J. Chem. Phys. 53, 1767 (1970).
(14) N. S. Shuman, M. A. Ochieng, B. Sztaray, and T. Baer, J. Phys. Chem. A 112, 5647
(2008).
(15)
P. B. Coates, Rev. Sci. Instrum. 63, 2084 (1992).
(16) T. Stephan, J. Zehnpfenning, and A. Benninghoven, J. Vac. Sci. Technol. A-Vac. Surf.
Films 12, 405 (1994).
(17)
M. N. Glukhovtsev, and R. D. Bach, Chem. Phys. Lett. 286, 51 (1998).
(18)
A. F. Lago, and T. Baer, J. Phys. Chem. A 110, 3036 (2006).
(19)
J. A. Blush, and P. Chen, J. Phys. Chem. 96, 4138 (1992).
(20)
M. W. Crofton, M. F. Jagod, B. D. Rehfuss, and T. Oka, J. Chem. Phys. 91, 5139 (1989).
(21)
F. P. Lossing, Can. J. Chem. 49, 357 (1971).
10
11
Tables
Table S1. Results from fits of the time traces for methyl and vinyl products from 193 nm
photolysis of MVK to a combined first- and second-order kinetic equation (eq. S2, see text for
details). Reported errors are 2 values.
methyl
vinyl
E (eV)
10.224
10.424
10.224
10.424
Si(t=0) (counts)
96.0  6.3
95.7  7.0
146.4  8.2
180.0  8.3
12
k1 (s-1)
13.2  12.6
0.4  14.0
70.0  17.0
88.9  15.5
k (s-1)
87.4  22.6
98.9  26.6
246.5  44.0
215.4  35.8
Table S2. Absolute photoionization cross-section of vinyl iodide measured relative to propene.
Photoionization
Energy (eV)
9.114
9.139
9.164
9.189
9.214
9.239
9.264
9.289
9.314
9.339
9.364
9.389
9.414
9.439
9.464
9.489
9.514
9.539
9.564
9.589
9.614
9.639
9.664
9.689
9.714
9.739
9.764
9.789
9.814
9.839
9.864
9.889
9.914
9.939
9.964
9.989
10.014
10.039
10.064
10.089
(E) (Mb)
0
0
0
0
0.30
0.19
0.39
0.77
3.20
7.15
6.90
5.81
7.93
13.20
11.17
25.77
26.41
16.24
16.54
17.27
13.02
16.19
20.69
30.94
20.74
21.92
18.67
27.60
24.74
25.14
29.67
24.87
26.96
25.11
25.28
25.72
25.89
25.69
25.23
26.67
Photoionization
Energy (eV)
10.114
10.139
10.164
10.189
10.214
10.239
10.264
10.289
10.314
10.339
10.364
10.389
10.414
10.439
10.464
10.489
10.514
10.539
10.564
10.589
10.614
10.639
10.664
10.689
10.714
10.739
10.764
10.789
10.814
10.839
10.864
10.889
10.914
10.939
10.964
10.989
11.014
11.039
13
(E) (Mb)
31.46
32.09
34.04
34.80
34.79
35.28
37.82
38.69
39.11
39.85
40.27
42.29
43.74
46.37
46.96
49.14
50.94
52.88
53.39
54.70
54.70
55.00
54.04
53.36
54.68
53.08
52.43
51.24
53.10
53.92
54.64
54.77
56.86
56.90
57.38
59.12
59.10
60.95
Table S3. Results from fits to the time traces for vinyl iodide and vinyl products at 10.013,
10.513, and 10.813 eV. Vinyl iodide signal levels are determined from the mean signal for the
single 13C isotopolog at m/z = 155 between 2 and 20 ms after photolysis whereas the vinyl signal
is determined at the instant of photolysis by fitting data to a combined first- and second-order
kinetic equation (eq. S2, see text for details). Reported errors are 2 uncertainties from the fitting
procedures.
E (eV)
vinyl iodide (13C)
vinyl radical
10.013
10.513
10.813
10.013
10.513
10.813
Si(avg), 2 –
20 ms
(counts)
1085  62
1251  65
972  56
-
Si(t=0)
(counts)
k1 (s-1)
k (s-1)
86  5
98  7
98  8
173  30
173  37
178  44
0  32
0  40
0  46
14
Table S4. Vinyl radical absolute photoionization spectrum obtained from a sum of the relative
MVK and VI spectra scaled to the five absolute cross-section measurements reported here.
Photoionization
Energy (eV)
8.549
8.574
8.599
8.624
8.649
8.674
8.699
8.724
8.749
8.774
8.799
8.824
8.849
8.874
8.899
8.924
8.949
8.974
8.999
9.024
9.049
9.074
9.099
9.124
9.149
9.174
9.199
9.224
9.249
9.274
9.299
9.324
9.349
9.374
9.399
9.424
9.449
9.474
(E) (Mb)
0.00
0.00
0.14
0.04
0.00
0.00
0.01
0.08
0.08
0.16
0.15
0.20
0.36
0.50
0.53
0.50
0.40
0.62
0.93
0.89
1.06
1.17
1.18
1.25
1.64
2.06
2.21
2.25
2.51
2.37
2.64
2.74
2.81
2.91
3.50
4.11
3.97
3.47
Photoionization
Energy (eV)
9.499
9.524
9.549
9.574
9.599
9.624
9.649
9.674
9.699
9.724
9.749
9.774
9.799
9.824
9.849
9.874
9.899
9.924
9.949
9.974
9.999
10.024
10.049
10.074
10.099
10.124
10.149
10.174
10.199
10.224
10.249
10.274
10.299
10.324
10.349
10.374
10.399
10.424
15
(E) (Mb)
3.05
3.18
3.62
5.40
5.72
4.86
4.84
3.84
3.69
4.72
5.99
6.06
5.76
5.76
5.49
5.82
6.03
6.38
5.92
5.58
6.56
7.13
7.15
6.34
6.17
5.55
6.14
7.95
8.31
7.39
7.06
7.57
7.23
7.72
8.72
8.11
7.52
8.28
Photoionization
Energy (eV)
10.449
10.474
10.499
10.524
10.549
10.574
10.599
10.624
10.649
10.674
10.699
10.724
10.749
10.774
10.799
10.824
10.849
10.874
10.899
10.924
10.949
10.974
10.999
11.024
11.049
(E) (Mb)
8.53
7.67
8.53
9.03
7.79
7.79
8.79
8.62
8.61
9.39
9.32
9.94
9.78
10.08
9.90
9.92
10.10
10.17
10.84
11.60
11.20
10.67
10.86
12.07
12.48
16
Figures
Intensity (Arb. Units)
m/z = 15
MVK + 193 nm
methyl radical
8.0
8.5
9.0
9.5
10.0
Photoionization Energy (eV)
10.5
11.0
Figure S1. Comparison of the m/z = 15 photoionization spectrum obtained from 193 nm
photolysis of MVK (black circles) with the known photoionization spectrum of the methyl
radical (ref. 7).
17
MVK + 193 nm, 10.224 eV
methyl (m/z = 15)
vinyl (m/z = 27)
120
Counts
100
80
60
40
20
0
0
10
20
Kinetic Time (ms)
30
40
160
MVK + 193 nm, 10.424 eV
methyl (m/z = 15)
vinyl (m/z = 27)
140
Counts
120
100
80
60
40
20
0
0
10
20
Kinetic Time (ms)
30
40
Figure S2. Time profiles for m/z = 15 (methyl, blue circles) and 27 (vinyl, red circles) obtained at
10.224 and 10.424 eV from photolysis of MVK. The solid lines indicate the corresponding fit to
a combined first- and second-order kinetic equation (eq. S2) used to determine the signal at the
instant of photolysis. The parameters obtained from the fitting procedure are presented in Table
S1.
18
1200
10.5 eV, 248 nm (70 mJ/pulse)
11
1000
800
Counts
-3
[C2H3I]0 = 9.4 x 10 cm
HI (m/z = 128) x10
I (m/z = 127)
600
400
200
0
0.0
0.5
1.0
Kinetic Time (ms)
1.5
2.0
50
Counts
40
30
20
10.5 eV, 248 nm (70 mJ/pulse)
10
11
[C2H3I]0 = 9.4 x 10 cm
HI (m/z = 128)
0
0
5
10
Kinetic Time (ms)
15
-3
20
Figure S3. Time profiles illustrating the strong spike in HI (blue) and I-atom (red) signal at early
time (upper panel) and the slow formation of HI at longer times (bottom panel) upon 248 nm
photolysis of vinyl iodide at 4 Torr and 298 K. Note that the intensity of the peak of the m/z =
128 spike near the instant following photolysis is clipped to illustrate the signal at later times.
19
1150
Counts
1100
1050
10.013 eV
vinyl (m/z = 27)
1000
13
C vinyl iodide (m/z = 155)
950
900
0
5
10
Kinetic Time (ms)
15
20
1300
Counts
1250
1200
10.513 eV
vinyl (m/z = 27)
1150
13
C vinyl iodide (m/z = 155)
1100
1050
0
5
10
Kinetic Time (ms)
15
20
1050
Counts
1000
950
900
10.813 eV
vinyl (m/z = 27)
13
C vinyl iodide (m/z = 155)
850
800
0
5
10
Kinetic Time (ms)
15
20
Figure S4. Kinetic traces and the corresponding fits to 13C signal of vinyl iodide (m/z = 155, red)
and vinyl radical (m/z = 27, blue) upon 248 nm photolysis of vinyl iodide at 4 Torr and 298 K.
Signal for the vinyl radical is vertically offset for comparison with the 13C vinyl iodide signal.
20