0

Two-color studies of CH3Br excitation dynamics

with MPI and Slice Imaging

Arnar Hafliðason1, Pavle Glodic2, Greta Koumarianou2,

Peter C. Samartzis2* and Ágúst Kvaran1*

1. Science Institute, University of Iceland, Dunhagi 3, 107 Reykjavík, Iceland.

2. Institute of Electronic Structure and Laser, Foundation for Research and Technology-

Hellas, Vassilika Vouton, 71110 Heraklion, Greece.

Supplementary material

Content: pages:

Fig. S1: KER spectra for Br+ and CH3 + for 2h = 67275 cm-1 showing

vibrational structure.................................................................................... 1

Fig. S2: Absorption spectrum from CH3Br in the energy region for

excitations to 5s/5s’ Rydberg states.....................................................….. 1

Fig. S3: Comparison of one-color KER spectra for Br+ ions shifted by

(3h ........................................................................................................ 2

Fig. S4 (a - e): Two color (pump/probe) KER spectra for Br+ / Br probing

along with anisotropic 2 values ......................................……….............. 3 – 5

Fig. S5 (a - e): Two color (pump/probe) KER spectra for Br+ / Br* probing

along with anisotropic 2 values ..................................…..……................ 6 – 8

Fig. S6 (a - b): KER spectra for Br/Br* probe-only excitations

along with anisotropic 2 values....................................………................. 9

Fig. S7 (a - c): Two color (pump/probe) KER spectra for CH3+ /

CH3(X; v1v2v3v4) probing along with anisotropic 2 value........................... 10 – 11

Fig. S8 (a - d): KER spectra for CH3(X; v1v2v3v4) probe-only excitations

along with anisotropic 2 values ................................……...……..…....... 12 – 13

Fig. S9: Ion signal intensity ratios vs. excitations……………….............. 14

Fig. S10: KERs for Pump/probe and “probing after pumping”................. 15 – 16

Fig. S11: Schematic representation for comparison of KERs.................... 17

Fig. S12: Schematic energy diagram for observed excitation processes

of CH3Br..................................................................................................... 18

Fig. S13: Energy diagrams and excitation processes of CH3Br.................. 19

Table. S1 a) - c): Anisotropy parameters.................................................. 20 – 22

Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics.This journal is © the Owner Societies 2019

1

Fig. S1

Fig. S1: KER spectra for Br+ (green) and CH3 + (black) for pump-only (2h = 67275 cm-1) showing

vibrational structures due to formation of CH3(3p2A2) in OPLA vibrational modes along with

Br/Br* (channel 3b; see Fig. S12). Corresponding thresholds for formation of CH3**(3p2A2) +

Br/Br* are indicated. Less laser power revealed the vibrational structure in Br+ KER.

Fig. S2

Fig. S2: Absorption spectrum for CH3Br in the energy region for excitations to 5s/5s’ Rydberg

states and relevant assignments (in black). Two-photon excitation wavenumbers and transitions

(𝜈𝑣′′𝑣′ ) used for probing CH3(X) are indicated in red.

2

Fig. S3

Fig. S3: Br+ kinetic energy release spectra (KERs) for pump-only.1 Two-photon excitation (2h)

wavenumbers are indicated at top. The spectra are normalized to the height of the lowest KER

spectra contributions, corresponding to channel 3b (see Fig. S12). The spectra are shifted by

(3h) (see explanation in Fig. S11) and plotted vertically as a function of the Three-photon

excitation wavenumber (y- axis to the lefts) and the total KER of the fragments CH3 and Br/Br* for

the spectrum of 2h = 79610 cm-1(y- axis to the right). Common energy thresholds for the formation

of CH3(X, v1v2v3v4) + Br/Br* after three-photon photodissociation of CH3Br via resonant excitation

to CH3Br Rydberg states are indicated at the bottom.

3

Fig. S4

Fig. S4-a: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 66019 cm-1 pumping

and Br probing.

Fig. S4-b: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 67275 cm-1 pumping

and Br probing.

4

Fig. S4

Fig. S4-c: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 68684 cm-1 pumping

and Br probing.

Fig. S4-d: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 72977 cm-1 pumping

and Br probing.

5

Fig. S4

Fig. S4-e: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 75905 cm-1 pumping

and Br probing.

6

Fig. S5

Fig. S5-a: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 66019 cm-1 pumping

and Br* probing.

Fig. S5-b: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 67275 cm-1 pumping

and Br* probing.

Ion inte

nsity

1.00.80.60.40.20.0

KERBr / eV

2 =

0.48

1.09

-1.0

b)

7

Fig. S5

Fig. S5-c: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 68684 cm-1 pumping

and Br* probing.

Fig. S5-d: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 72977 cm-1 pumping

and Br* probing.

8

Fig. S5

Fig. S5-e: Pump/probe Br+ KER spectrum and anisotropic 2 values. 2hv = 75905 cm-1 pumping

and Br* probing.

9

Fig. S6

Fig. S6-a: Probe-only Br+ KER spectrum and anisotropic 2 value for Br. 2h = 75009 cm-1

probing.

Fig. S6-b: Probe-only Br+ KER spectrum and anisotropic 2 value for Br*. 2h = 74991 cm-1

probing.

Ion inte

nsity

1.00.80.60.40.20.0

KERBr / eV

2 =

0.06

a)

Ion in

ten

sity

1.00.80.60.40.20.0

KERBr / eV

2 =

1.98

b)

10

Fig. S7

Fig. S7-a: Pump/probe CH3+ KER spectrum and anisotropic 2 values. 2hv = 72977 cm-1

pumping and CH3 (2h = 60698 cm-1; 211). probing.

Fig. S7-b: Pump/probe CH3+ KER spectrum and anisotropic 2 values. 2hv = 78370 cm-1

pumping and CH3 (2h = 59972 cm-1; 000). probing.

11

Fig. S7

Fig. S7-c: Pump/probe CH3+ KER spectrum and anisotropic 2 values. 2hv = 79610 cm-1

pumping and CH3 (2h = 59972 cm-1; 000) probing.

12

Fig. S8

Fig. S8-a: Probe-only CH3+ KER spectrum and anisotropic 2 value for CH3 (2h = 59972 cm-

1; 000) probing.

Fig. S8-b: Probe-only CH3+ KER spectrum and anisotropic 2 value for CH3 (2h = 59898 cm-

1; 111) probing.

2 = 0.98

a)

Ion inte

nsity

1.41.21.00.80.60.40.20.0

KERCH3 / eV

2 = 1.40

b)

Ion in

ten

sity

1.41.21.00.80.60.40.20.0

KERCH3 / eV

13

Fig. S8

Fig. S8-c: Probe-only CH3+ KER spectrum and anisotropic 2 value for CH3 (2h= 60698 cm-

1; 211) probing.

Fig. S8-d: Probe-only CH3+ KER spectrum and anisotropic 2 value for CH3 (2h=61387 cm-

1; 222) probing.

2 = 0.90

c)

Ion in

ten

sity

1.41.21.00.80.60.40.20.0

KERCH3 / eV

2 = 0.97

d)

Ion in

ten

sity

1.41.21.00.80.60.40.20.0

KERCH3 / eV

14

Fig. S9

Fig. S9: Ion signal intensity ratios for masses I(Br+)/I(CH3+) (red open squares) and

I(CH+)/I(CH3+) (blue open circles) as a function of two-photon excitation wavenumber, along with

the MPI spectrum from CH3+ ions. The threshold for ion-pair formation (CH3

+ + Br–) is indicated

as a black vertical broken line.

M+= Br+

M+= CH+

I(M+)/

I(CH3+) CH3

+

+

Br–

15

Fig.S10

Fig. S10-a: Br+ kinetic energy release spectra (KERs) for pump/probe (black) and “probing after

pumping”(grey) for 2hv = 68684 cm-1 pumping and Br* probing. The “probing after pumping”

spectrum was derived by subtraction pump-only and probe-only spectra from the pump/probe

spectrum.

Fig. S10-b: Br+ kinetic energy release spectra (KERs) for pump/probe (black) and “probing after

pumping”(grey) for 2hv = 67275 cm-1 pumping and Br probing. The “probing after pumping”

spectrum was derived by subtraction pump-only and probe-only spectra from the pump/probe

spectrum.

16

Fig.S10

Fig. S10-c: CH3+ kinetic energy release spectra (KERs) for pump/probe (black) and “probing after

pumping”(grey) for 2hv = 78370 cm-1 pumping and CH3 (2h = 59972 cm-1; 000) probing. The

“probing after pumping” spectrum was derived by subtraction pump-only and probe-only spectra

from the pump/probe spectrum.

17

Fig.S11

Fig. S11: Schematic representation for convenient comparison of two KER spectra (see for

example S3) attained from two different excitation frequencies, v0 and vi (vertical purple and blue

arrows) with respect to a two-photo-dissociation process (CH3Br + 2hv → CH3Br** → CH3(X) +

Br*). The spectra are shifted by (2h), for (2h) = 2hi - 2h0, where 0 and i are photon

excitation frequencies of a reference spectrum (0) and a spectrum i (i). The two-photon excitation

energy is presented along the y-axis (to the left) and the shifted KERs tilted to the right (plotted

vertically) to give increasing KER values downwards along the y-axis (see y-axis to the right). The

‘‘zero kinetic energy released’’ for the KER of the highest excitation energy (2h0) is set to zero.

Now spectral features due to the formation of the same energy species (CH3(X, v1v2v3v4) + Br*),

after two-photon excitation and corresponding thresholds will match.

18

Fig. S12

Fig. S12: Schematic energy diagram for observed excitation processes of CH3Br prior to this work.

Vertical black arrows: photoexcitations. Other arrows: fragmentation (dissociation (1,2,3b,3c,4)

and autoionization (3a)) processes involving two-photon resonant excitations to s (broken lines)2

and p/d (solid lines)1 Rydberg states. CH3Br(X), CH3Br*, CH3Br**(Ry) and CH3Br#: Ground-,

valence-, Rydberg- and superexcited state. Charged particles (ions, electrons) detected are marked

by red circles.

19

Fig. S13

Fig. S13 a) and b): Semi-schematic energy diagrams and excitation processes of CH3Br leading

to CH3+ and Br+ formation based on this work and references [1] (a) and [2] (b) showing relevant

energy thresholds (horizontal lines), photoexcitations (vertical arrows) and fragmentation

(dissociations and autoionization) channels (black bended arrows). The number of photons (n = 1

– 4) in photoexcitations prior to dissociations are indicated in boxes. Vertical arrows in (a) are for

the two-photon resonance excitations (2h) 66019 cm-1(red) and 72977 cm-1 (purple). Vertical

arrows in (b) are excitations corresponding to the 111 (red) and 22

2 (purple) CH3(X) resonances.

The one-photon absorption spectrum of CH3Br 3, 4 is tilted to the right in the figures.

a)

20

Table.S1 a): Anisotropy parameter () from figures S4, S5, S6, S7 and S8 and major fragmentation channels (see Fig. S12).

Br

Probing

Figure a) 2 h/ cm-1 b) KER / eV c)

Major

Channels d) 2 4 6

S4-a 66019 0.08-0.20 3b 0.24 ±0.01 -0.04 ±0.01 0.04 ±0.01

0.22-0.33 1 0.18 ±0.01 -0.02 ±0.01 0.00 ±0.01

0.43-0.53 2 -0.44 ±0.01 0.14 ±0.02 0.01 ±0.02

S4-b 67275 0.08-0.15 3b 0.15 ±0.02 -0.11 ±0.02 0.06 ±0.02

0.22-0.27 1 -0.06 ±0.01 -0.08 ±0.01 0.01 ±0.01

0.39-0.61 2 -0.55 ±0.02 0.04 ±0.02 0.04 ±0.02

S4-c 68684 0.07-0.10 3b 0.20 ±0.02 -0.08 ±0.03 -0.02 ±0.03

0.22-0.27 1 0.11 ±0.01 0.00 ±0.02 0.04 ±0.02

0.39-0.53 2 -0.34 ±0.01 0.08 ±0.03 0.14 ±0.03

S4-d 72977 0.07-0.13 3b 0.44 ±0.01 0.00 ±0.01 -0.02 ±0.01

0.22-0.27 1 0.34 ±0.01 0.05 ±0.01 -0.02 ±0.01

0.39-0.53 2 0.45 ±0.01 0.03 ±0.01 0.03 ±0.01

S4-e 75905 0.07-0.10 3b 0.21 ±0.02 -0.03 ±0.02 0.03 ±0.02

0.22-0.27 1 0.04 ±0.02 -0.05 ±0.02 0.03 ±0.02

0.39-0.53 2 0.66 ±0.05 -0.04 ±0.06 0.02 ±0.07

S6-a 75009 0.20-0.25 1 0.06 ±0.04 -- -- -- -- a) Corresponding figure in ESI, b) 2h excitation energy, c) KER region inspected for parameter d) Fragmentation channels before ionization shown in fig.S12.

21

Table.S1 b): Anisotropy parameter () from figures S4, S5, S6, S7 and S8 and major fragmentation channels (see Fig. S12).

Br*

Probing

Figure a) 2 h/ cm-1 b) KER / eV c)

Major

Channels d) 2 4 6

S5-a 66019 0.07-0.10 3b 0.65 ±0.02 -0.08 ±0.02 -0.06 ±0.02

0.17-0.22 1 1.06 ±0.03 -0.02 ±0.03 -0.05 ±0.03

0.53-0.65 2 -1.00 ±0.02 0.37 ±0.02 -0.01 ±0.02

S5-b 67275 0.07-0.10 3b 0.48 ±0.02 -0.21 ±0.02 0.00 ±0.03

0.17-0.22 1 1.09 ±0.03 -0.03 ±0.03 -0.09 ±0.03

0.53-0.65 2 -1.00 ±0.03 0.46 ±0.03 -0.08 ±0.03

S5-c 68684 0.07-0.10 3b 0.56 ±0.04 -0.13 ±0.05 0.04 ±0.05

0.17-0.22 1 0.89 ±0.05 0.00 ±0.06 -0.16 ±0.06

0.53-0.65 2 -1.00 ±0.03 0.16 ±0.03 0.10 ±0.03

S5-d 72977 0.07-0.10 3b 0.76 ±0.01 0.04 ±0.01 -0.01 ±0.01

0.17-0.22 1 1.08 ±0.01 0.04 ±0.01 0.00 ±0.01

0.46-0.61 2 0.38 ±0.01 0.04 ±0.01 -0.06 ±0.01

S5-e 75905 0.07-0.10 3b 0.53 ±0.02 -0.05 ±0.03 -0.01 ±0.03

0.17-0.22 1 1.52 ±0.04 0.14 ±0.03 -0.13 ±0.03

0.46-0.61 2 0.40 ±0.02 0.01 ±0.02 0.00 ±0.02

S6-b 74991 0.16-0.21 1 1.98 ±0.06 -- -- -- -- a) Corresponding figure in ESI, b) 2h excitation energy, c) KER region inspected for parameter d) Fragmentation channels before ionization shown in fig. S12.

22

Table.S1 c): Anisotropy parameter () from figures S4, S5, S6, S7 and S8 and major fragmentation channels (see Fig. S12).

CH3

Probing

Figure a) 2 h/ cm-1 b) KER / eV c)

Major

Channelsd) 2 4 6 Prob. excita.e)

S7-a 72977 0.24-0.69 3b 0.84 ±0.03 -0.26 ±0.04 -0.01 ±0.04 211

0.95-1.12 1(Br*)? f) 1.15 ±0.06 -0.41 ±0.06 0.19 ±0.07 211

1.24-1.50 1(Br)? f) 0.69 ±0.06 0.03 ±0.07 0.32 ±0.08 211

S7-b 78370 0.10-0.70 3b 0.69 ±0.03 -0.13 ±0.03 0.02 ±0.04 000

1.08-1.25 1(Br*) 1.10 ±0.02 -0.04 ±0.02 0.02 ±0.02 000

1.46-1.63 1(Br) -0.40 ±0.04 0.13 ±0.06 -0.03 ±0.06 000

S7-c 79610 0.17-0.72 3b 0.72 ±0.03 -0.34 ±0.03 0.04 ±0.03 000

1.20-1.36 1(Br*) 0.99 ±0.06 -0.22 ±0.07 0.18 ±0.07 000

1.55-1.65 1(Br) -0.93 ±0.02 0.54 ±0.02 -0.21 ±0.02 000

S8-a 59972 0.08-0.66 3a, 4 0.98 ±0.15 -- -- -- -- 000

S8-b 59898 0.13-0.72 3a, 4 1.40 ±0.20 -- -- -- -- 111

S8-c 60698 0.18-0.75 3a, 4 0.90 ±0.06 -- -- -- -- 211

S8-d 61387 0.13-0.71 3a, 4 0.97 ±0.15 -- -- -- -- 222

a) Corresponding figure in ESI, b) 2h excitation energy, c) KER region inspected for parameter d) Fragmentation channels before ionization shown in fig.S12, e) Probing excitation, 𝜈𝜐′′

𝜐′ where, 𝜈: vibrational mode, 𝜐′: vibrational

level in excited state and 𝜐′′: vibrational level in ground state f) assignment uncertain

23

References

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2009, 11, 2234-2240.

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2672-2676.

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