Supplementary Material for
Photoelectron Spectroscopy of the Thiazate (NSO–) and Thionitrite (SNO–)
Isomer Anions
Julia H. Lehman1,2,* and W. Carl Lineberger1,*
1
JILA and Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309, United States
of America
2
Present address: School of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom
*Corresponding Authors: [email protected], [email protected]
Table of Contents
I. Photoelectron spectrum of NSO– using 338 nm photons .................................................................. S1
II. Descriptions of the NSO and NSO– vibrational modes...................................................................... S2
III. Simulated Photoelectron Spectrum of NOS– ................................................................................... S5
I. Photoelectron spectrum of NSO– using 338 nm photons
The near-threshold cross-section for photodetachment depends on the electron kinetic energy as
well as the angular momentum of the (atomic-like) orbital from which the electron is detached,
where 𝜎~(𝑒𝐾𝐸)ℓ+1⁄2. For NSO–, the intensity of the peaks close to threshold are attenuated when
using 3.4945 eV photons. For example, using 3.669 eV (~338 nm) photon energy instead of 3.4945
eV photon energy, the relative integrated intensity of peak i compared to the EA peak approximately
doubled. The eKE of peak i changed from approximately 80 meV to 250 meV in going from 3.4945 eV
to 3.669 eV photon energy. The integrated intensity of the second largest peak in the spectrum
(peak e) remains about the same relative to the EA (increased by a factor of 1.1). This is seen in Fig.
S1.
S1
Fig. S1. Comparison of the NSO– photoelectron spectrum using 355 nm (black) and 338 nm (red). The
338 nm spectrum has more noise, due to a shorter integration time, but compares well with the 355
nm spectrum. The two spectra are scaled so that the amplitude of the EA peaks are the same. Note
that the red spectrum will have slightly broader peaks than the black spectrum due to the degrading
resolution with increasing eKE.
II. Descriptions of the NSO– and NSO vibrational modes
Because of the inconsistent labeling in past publications, the following two tables aim to clarify what
is meant by the descriptions of 1, 2, and 3 for the NSO– and NSO vibrational modes. The calculated
harmonic frequencies, displacement vectors, and the displacement coordinate matrices are listed in
Tables S1 and S2. These are calculated at the B3LYP/aug-cc-pVQZ level of theory. Additional levels of
theory were used to check for consistency. For example, using a Pople basis set instead of a Dunning
basis set yielded the same labeling results (B3LYP/6-311++G(d,p)), where 1 and 2 were the
asymmetric and symmetric stretch, respectively. A different method was also used (CCSD(T)/aug-ccpVQZ) and again yielded the same labeling listed here. While this is certainly not an exhaustive
theoretical exploration, it lends credence to the labeling we adopted in this work.
S2
Table S1. Calculated frequencies, displacement vectors, and x-y displacement coordinates of the
three vibrational modes in the NSO– anion, calculated using B3LYP/aug-cc-pVQZ.
1
1283.8 cm-1
Asymmetric stretch
(note that the oxygen atom
displacement vector is beneath
its bond with sulfur)
2
993.2 cm-1
Symmetric Stretch
3
486.8 cm-1
Bend
S3
N
S
O
X
0.82
-0.44
0.17
Y
-0.30
0.07
0.13
N
S
O
X
0.35
0.18
-0.66
Y
-0.16
0.33
-0.52
N
S
O
X
0.43
0.07
-0.52
Y
0.54
-0.39
0.31
Table S2. Calculated frequencies, displacement vectors, and x-y displacement coordinates of the
three vibrational modes in the NSO radical neutral, calculated using ROB3LYP/aug-cc-pVQZ.
1
1199.1 cm-1
Asymmetric Stretch
(note that the nitrogen
atom displacement
vector is directly beneath
its bond with sulfur)
2
1017.2 cm-1
Symmetric stretch
3
313.9 cm-1
Bend
S4
N
S
O
X
-0.39
0.48
-0.62
Y
0.14
0.16
-0.44
N
S
O
X
0.79
-0.13
-0.42
Y
-0.28
0.23
-0.22
N
S
O
X
0.35
0.08
-0.47
Y
0.55
-0.44
0.39
III. Simulated Photoelectron Spectrum of NOS–
Table S3 lists the anion and neutral NOS geometries and harmonic frequencies, calculated at the
B3LYP/aug-cc-pVQZ level of theory. The NOS– isomer could also be formed in our ion source,
although it is highly unlikely given the energetic arguments presented in the main text. In addition,
the S-ON bond length in the anion is significantly extended, approximately 0.3 Å longer than the SNO bond length in the SNO– anion, which is suggestive of the weakness of the S-ON bond in the
anion and the possibility of the extra electron localizing on the S– moiety. The S-ON bond length is
also the largest geometry change between the anion and neutral equilibrium geometries, so this
would give rise to significant Franck-Condon activity in the S-ON stretch. Fig. S2 shows the simulated
photoelectron spectrum overlaid on the experimental spectrum, with the EA(NOS) at the calculated
value (2.183 eV). There is an extended progression in the S-ON stretch, as expected, along with
activity in the NOS bend. This leads to two overlapping progressions with alternating peak intensities
at the low eBE portion of the spectrum, which become comparable in intensity at high eBE portions
of the spectrum. While the overall simulated spectrum matches the experimental spectrum breadth
and position fairly well, recall that the simulated photoelectron spectrum uses the harmonic
approximation and harmonic frequencies. This will significantly affect the simulated spectrum,
particularly since the peak of this simulation corresponds to approximately 8 quanta in the S-ON
stretch. This suggests that the low eBE portion of the spectrum could provide a more accurate
comparison between experiment and theory than the high eBE side of the spectrum. As such, Fig. S3
shows the higher resolution experimental data overlaid with the NOS– photoelectron spectrum
simulation at the low eBE portion of the spectrum. Notice that the pattern of the peaks do not
match the experiment as well as the SNO– simulated spectrum. There are more peaks in the
experiment than can be found in the NOS– photoelectron spectrum simulation. Again, the low eBE
portion of the spectrum should be a better indicator of the overall agreement between experiment
and theory. The combination of this disagreement between the simulation and the experimental
spectrum, along with the energetic arguments presented in the main text, leads us to conclude that
SNO– is likely the primary contributor to the m/z = 62 photoelectron spectrum.
Table S3. Calculated geometries and harmonic frequencies for NOS– and NOS (B3LYP/aug-cc-pVQZ,
ROB3LYP for the neutral radical). The difference between the anion and neutral geometries are
shown in the third column, with the percentage change from the anion shown in parentheses. The
calculated electron affinity (EA) for NOS is also included.
NOS–
NOS
(Anion-Neutral)
r(N-OS) / Å
1.170
1.210
-0.040 (-3.4%)
r(NO-S) / Å
2.063
1.723
0.340 (16.5%)
∠(NOS) / °
124.9
130.1
-5.2 (-4.2%)
1 / cm-1
1625.8
1171.3
–
2 / cm-1
512.0
524.4
–
3 / cm-1
267.8
278.0
–
EA / eV
–
2.183
–
S5
Fig. S2. Experimental photoelectron spectrum of m/z = 62 using 355 nm (3.49 eV) photon energy,
shown in black. The calculated Franck-Condon factors for NOS– photodetachment are shown as blue
sticks. The convolution of the Franck-Condon factors with the experimental resolution is shown as a
red line.
S6
Fig. S3. Experimental photoelectron spectrum of m/z = 62 using 478 nm (2.596 eV) photon energy,
shown in black. The peaks between 2 and 2.15 eV are due to photodetachment from S–. The
calculated Franck-Condon factors for the photodetachment from NOS– are shown as blue sticks. The
convolution of the Franck-Condon factors with the experimental resolution is shown as the red line.
Notice that there are peaks in the experiment that are not recovered by the simulation, particularly
the multiplets discussed in the main text. The narrow peaks in the simulation should have been fully
resolved in the experiment if this spectrum was indeed able to be attributed to NOS–.
S7