CH3Br VMI-REMPI studies in combination with Mass resolved REMPI;

Summary report (July, 2017) for experimental data from FORTH and analysis from 2016.

NB: processed data and data analysis are to be found under https://notendur.hi.is/~agust/rannsoknir/Crete/Crete-1.htm

Content list:

Topics: pages:I. Mass Resolved (MR)-REMPI and VMI-REMPI….. 2 – 151) MR-REMPI……………………………………. 2 - 32) VMI-REMPI; one-color (CHn

+, Br+, CBr+)….. 4 – 133) VMI-REMPI; one-color (e- detection)………… 14-184) VMI-REMPI; two-color (Br/Br* detection)…… 19-235) VMI-REMPI; two-color (CH3 detection)……. 24

Updated: 170809 / IN PROGRESS

1

I. Mass Resolved REMPI (MR-REMPI) and VMI-REMPI

1) MR-REMPI:Results:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx slides 7, 14-16(see also: https://notendur.hi.is/~agust/rannsoknir/papers/jpcA114-9991-10.pdf ; Fig. 1a):Mass spectra and corresponding REMPI spectra have been recorded for the one-color excitation corresponding to two-photon resonance excitation within the range of 66000 – 80000 cm-1:

82

80

78

76

74

72

70

68

66

x103

13 15 79 91

iBr+ (i=79,81) CBr+ (i=79,81)

CHn+

n=1,2,3

Intensity Mw / amu

E / cm-1

CH3+ + Br-

x 2.5

Fig 1a: Mass spectra vs. CH3+-REMPI spectra. The mass spectra are normalized to

a common intensity for the CH3+ peaks.

Conclusions:

Strongest mass signals are observed for the CH3+ ion

(see Fig. 1a above and slides 15-16 in https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx )

Relative signal contributions of other ions (I(M+)/I(CH3+)); M = CH2,CH, Br)

increases as the 2hv scale approaches the CH3+ + Br- threshold

(see Fig. 1a above and https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptxslides 15-16)

2

The CH3+-REMPI spectrum can be divided into two major contributions, depending on

the ion formation mechanisms (this is further supported by one-color VMI_REMPI data below), i.e. i) „an underlying „continuum“ contribution“, gradually increasing with 2h, which is due to one-photon photodissociation process (1hv excitation to repulsive valence states) followed by three-photon (3hv) nonresonance ionization of CH3 (marked as 1h) AND ii) „Rydberg state spectra contributions“ on top of (i), which is due to initial two-photon resonance excitations to Rydberg states (marked as 2hr):https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx; slide 52:

80000780007600074000720007000068000660002h / [cm-1]

[3/2]np;w

[1/2]np;w

[3/2]nd;w

[1/2]nd;w

5 6 70 0 02

n =

w =5 602

02

0

02

02

02

02

4 6

4 5

3 2 1 3 2

3 2

3 2 1

3 2

6601

9

6868

4

6846

1

7265

5

7297

7

7541

875

686

7590

5

7822

5

7837

0

7819

3

7840

1

7961

0

8064

080

758

8067

4

8088

12hvr:signals followingtwo-photonresonance excitation

1hv:Signals followingone-photon excitation

Fig. 1bsee also https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptxslide 5 (top)

3

2) Results: VMI-REMPI data were collected for one color excitation corresponding to two-

photon excitation to number of Rydberg states within the range of 66000 – 80000 cm-1, for twelve wavenumber values in total:https ://notendur.hi.is/~ agust/rannsoknir/Crete16/XLS-160912.xlsx ; sheet: „Waves“:

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx ; slide 17:

80000780007600074000720007000068000660002h / [cm-1]

[3/2]np;w

[1/2]np;w

[3/2]nd;w

[1/2]nd;w

5 6 70 0 02

n =

w =5 602

02

0

02

02

02

02

4 6

4 5

3 2 1 3 2

3 2

3 2 1

3 2

6601

9

6868

4

6846

1

7265

5

7297

7

7541

875

686

7590

5

7822

5

7837

0

7819

3

7840

1

7961

0

8064

080

758

8067

4

8088

1

6650

3

6727

5

6888

2

6994

7

7424

9

7668

977

165

Fig. 2aImages for CHn

+; n = 3-0, Br+ and CBr+ ions were detected and recorded to a different amount:https ://notendur.hi.is/~ agust/rannsoknir/Crete16/XLS-160912.xlsx ; sheet: „Waves“:„Wave number“ entries in the table , below, represent measurements which were performed (red shaded areas represent „nonexisting measurements“):

4

KER spectra and angular distributions were derived from the images:KER spectra: See processed data: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx; slides 2 - 64See assignments/KER spectra predictions: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160922-CH3Br(2).pptx; Angular distributions: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx; slides 65-109

Conclusions concerning the strongest ion signals (i.e. CH3+):

CH3+ KERs (use xx KERs):

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx ; slide 10:

10

8

6

4

2

0

2.01.51.00.50.0

CH3+

eV

CH3++Br-

Ry(2hv/cm-1):

79610 (16.09.16)78370(12.9.16)77165(15.9.16)75905(14.9.16)74249815.9.16)72973(7.9.16)68684(14.9.16)67275(13.9.16))66503(8.9.16)66019 (6.9.16)

Fig. 2b

5

Some of the KERs show two major contributions according to the two different ion formation mechanisms (i) and (ii) (see (1); conclusion above) (ii) broad „underlying“ continuum feature corresponding to 2hr (ii) and (i) sharp peaks on top :https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx; slide 64:

3.0

2.5

2.0

1.5

1.0

0.5

0.0

2.52.01.51.00.50.0

2hvr:signals followingtwo-photonresonance excitation

1hv:Signals followingone-photon excitation

77165 (15.09.16)

eV

Example of a1hv and 1hvrsignal contributions in a CH3 KER spectrum:

Fig 2c 2hr (ii) spectral contributions:

a) The lowest energy excitation KERs (2h = 66019– 68684 cm-1) show vibrational structure in the 2hr spectra (ii). This is due to the following CH3

+ ion formation:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx; slide 18:

CH3Br

CH3Br** (Ry)

CH3**(v´+n) + Br/Br*:CH3**(v´) + Br/Br*

CH3+ + Br/Br*

Vibrational ladder for The OPLA vibrationalmode

Molecularexcitation

Dissoci-ation

Fragmentionization

KER

Intensity

2hvr

1hvpd

1hvi

Fig. 2di.e. two-photon resonance excitation to a Rydberg states (2hr) followed by one-photon photodissociation via a superexcited state (1hpd) followed by one-photon

6

ionization (1hi) of CH3**(3p2A2): (2hr+1hpd +1hi) REMPI. NB: The mechanism involves three-photon excitation (3h = 2hr+1hpd ) prior to the dissociation.b) The higher energy excitation KERs (2h > 68684 cm-1) involve analogous ion formation mechanisms to that described in (a) including CH3** fragments of higher energy than CH3**(3p2A2) as well. (see: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx; slide 41 for the energetics AND https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx ; slide 28 for CH3** states) NB: This is further confirmed by PES (see below).

Since the two spectral contributions (i) and (ii) involve one-photon (1h) and three-photon (3h) excitations prior to dissociation it is convenient to compare the KERs on two different h scales, (i) where KERs, for excitation frequencies i, have been shifted by h = h = h(0 – i) with respect to a reference spectrum (excitation frequency 0) AND (ii) where the KERs have been shifted by 3h = 3h = 3h(0 – i). This corresponds to a normalization of the spectra of same formation mechanism ((i) or (ii)) with respect to energy thresholds of fragment species. (analogous comparison is performed in references https://notendur.hi.is/~agust/rannsoknir/papers/jcp130-034304-09.pdf (Fig6) and https://notendur.hi.is/~agust/rannsoknir/papers/pccp11-2234-09.pdf (Fig.6)): https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx;slide 53:Thus:

Threshold (2)

Threshold (1)

nhv

exci

tatio

nsn

= 1,

2,3,

…

KER spectra

3h0 Relative intensity

Fig. 2ehttps://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx;slide 54:Thus, for (ii):

7

151050

43

21

03h/eV

CH3(3p2A2)+Br

CH3(3d2E)+Br

CH3(3d2A1)+Br

CH3(4p2A2)+Br

CH3(4f2E)+Br

3hv

exci

tatio

ns

Thresholds

CH3(3p2A2)+Br*

CH3(3d2E)+Br*

CH3(3d2A1)+Br*

CH3(4p2A2)+Br*

CH3(4f2E)+Br*

79610 (16.09.16)78370(12.9.16)77165(15.9.16)75905(14.9.16)74249815.9.16)

72973(7.9.16)68684(14.9.16)67275(13.9.16))66503(8.9.16)66019 (6.9.16)

Fig. 2f

1h (i) spectral contributions:The highest energy excitation KERs (2h = 77165– 79610 cm-1) show sharp peaks, particularely so for 2h = 77165 and 79610 cm-1, for which the 1h(i) ion formation contribution is the major (2hvr(ii) minor) as can be seen from the CH3+ REMPI spectrum (see Fig 2a above) These are due to the following ion formation:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx;slide 43:

120

100

80

60

40

20

0

x103

16141210864

CH3Br

CH3 + Br/Br*

CH3+ + Br-

CH3Br+/CH3Br+*

CH3** + Br/Br*

CH3+ + Br/Br*

r/A

1h

3hi

Fig. 2g

8

i.e. one-photon photodissociation (1hph) to form CH3(v1,v2,v3,v4) + Br/Br* followed by three-photon (two-photon for 2h = 79610 cm-1;NB) nonresonance ionization (3hi (2hi)) of CH3(v1,v2,v3,v4): (1hpd + 3hi(2hi)) REMPI:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx;slide 55:

151050

2.52.0

1.51.0

0.50.0

h/eV

CH3(0000)+Br(1.5856)CH3(0100)+Br(1.5224)

(1.4394)CH3(0001)+Br(1.2725)CH3(1000)+Br

(1.2562)CH3(0010)+Br

Thresholds

CH3(0000)+Br*(1.2016)

CH3(0100)+Br*(1.1384)CH3(0001)+Br*(1.0555)

CH3(1000)+Br*(0.8885)

CH3(0010)+Br*(0.8722)

79610 (16.09.16)78370(12.9.16)77165(15.9.16)75905(14.9.16)74249815.9.16)

72973(7.9.16)68684(14.9.16)67275(13.9.16))66503(8.9.16)66019 (6.9.16)

1hv

exci

tatio

ns

Hot bands, i.e. due toVibrationall „hot“ CH3Br#

Fig. 2h

Vibrational analysis of the lowest energy excitation KERs (2h = 66019, 66503, 67275, 68684 cm-1) revealed vibrational spectroscopic parameters for the CH3** (3p 2A2) Rydberg state, vibrational mode 2 / OPLA:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx;slides 58, 65-68:

1.0

0.8

0.6

0.4

0.2

0.0

2.01.51.00.50.0

v=012345678910111213

we=1310.3 cm-1

wexe= 10.648 cm-1

D0= 24 164 cm-1

3p 2A2

D0 stands for CH3Br -> CH3 + Br

66503 cm-1

eV Fig, 2i

9

The we parameter (1310 cm-1) is to be compared with corresponding values reported in NIST(http://webbook.nist.gov/ ) for CH3**(3p 2A2), CH3

+(X) of 1323 and 1359 +/- 7 cm-1 respectively. we for CH3(X) on the other hand is significantly lower (606 cm-1; http://webbook.nist.gov/)(see also: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx slides 27, 28, 45)

Conclusions concerning the strongest ion signals (i.e. CH3+):

CH3+ angular distributions (xx signals):

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx ;slide 81: The angular distributions of the CH3

+ images, corresponding to the 2hr (ii) ion formation mechanisms, display shapes corresponding to parallel to “neutral” (i.e. equal parallel and perpendicular character) transitions.https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx;slide 82:Anisotropy parameters ( 2) extracted from the angular distributions as a function of the two-photon excitation wavenumber are in the range of about 0 to 2. a) Medium values of about 0.7 – 2.0 are derived for excitations to the four lowest states (2h = 66019, 66503, 67275, 68684 cm-1), which involve a dominant ionization of the CH3**(3p 2A2) Rydberg state following two-photon resonance excitation (2hr) to CH3Br (5p) Rydberg states and a further one-photon photodissociation (1hpd) step. b) A large 2 value of about 2.0, corresponding to a purely parallel transition, is derived for excitation to the 2h = 72911 cm-1 state which involves a dominant ionization of the CH3**(3d 2E) and/or CH3**(3d 2A1) Rydberg states (see (3) below) following two-photon resonance excitation (2hr) to CH3Br (4d) Rydberg states and a further one-photon photodissociation (1hpd) step. c) Close to zero vales of 2, corresponding to “neutral” transition are derived for excitations to the states 2h = 75905 and 79610 cm-1 state, which involve two-photon resonance excitation (2hr) to CH3Br (6p) and (7p) Rydberg states.

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

78767472706866x103

2

1.2932 660190.71411 665031.1593 672750.71876 686842.0226 729771.3393 74249-0.058 759050.5568 771650.2957 783700.0092239 79610

CH3+

Fig. 2j

10

The sharp peaks due to the 1h(i) ion formation mechanism (see Fig. 2h) which appear near h = 1.5 eV are due to formation of CH3(bending modes, n2,n4) + Br (ground state) after 1hpd. Angular distributions of the CH3

+ fragments are perpendicular () in nature with 2 = -0.15 and -0.24 for 2h = 77165 cm-1 and 79610 cm-1, respectively:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx; slide 79,80:

3.5

3.0

2.5

2.0

1.5

1.0

0.5

150100500

3.0

2.5

2.0

1.5

1.0

0.5

0.0

2.52.01.51.00.50.0 eV

q

2 = 0.5568

2 = 0.89093

2 = -0.14974

2 = 1.0978

2 = 1.5678

Ry(2hv/cm-1):77165(15.9.16)

XZ

CH3+

Fig. 2k

3.5

3.0

2.5

2.0

1.5

1.0

150100500

8

6

4

2

0

2.52.01.51.00.50.0eV

q

2 = 0.0092239

2 = 1.8876

2 = 1.4666

2 = -0.23585

2 = 1.4741

Ry(2hv/cm-1):79610(16.9.16)

XZ

CH3+

Fig. 2lThis suggests that the major 1hpd transition corresponds to excitation of CH3Br to the repulsive state 3Q1 and/or to the 1Q1 state (both of which are perpendicular transitions) followed by a dissociation on the diabatic curves to form CH3(bending modes) + Br:https://notendur.hi.is/agust/rannsoknir/papers/pccp1-747-00.pdf

11

The sharp peaks due to the 1h(i) ion formation mechanism (see Fig. 2h) which appear near h = 1.26 eV are due to formation of CH3(stretching modes, 1,3) + Br (ground state) after 1hpd. Angular distributions of the CH3

+ fragments are parallel () in nature (see Figs, 2k and 2l above) with 2 = +0.89 and +1.47 for 2h = 77165 cm-1 and 79610 cm-1, respectively. This suggests that the major 1hpd transition corresponds to excitation of CH3Br to the repulsive state 3Q0 followed by a dissociation on the adiabatic curves to form CH3(stretch modes) + Br:https://notendur.hi.is/agust/rannsoknir/papers/pccp1-747-00.pdf

The sharp peaks due to the 1h(i) ion formation mechanism (see Fig. 2h) which appear near h = 1.14 eV are due to formation of CH3(bending modes, 2) + Br* (SO excited state) after 1hpd. Angular distributions of the CH3

+ fragments are almost purely parallel () in nature (see Fig. 2l above) with 2 = +1..89 for 2h = 79610 cm-1. This suggests that the major 1hpd transition corresponds to excitation of CH3Br to the repulsive state 3Q0 followed by a dissociation on the diabatic curves to form CH3(bending mode) + Br*:https://notendur.hi.is/agust/rannsoknir/papers/pccp1-747-00.pdf

Conclusions concerning the Br+ ion signalsBr+ KERs (use xx KERs):

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx ; slide 28:

4

3

2

1

0

2.52.01.51.00.50.0

79Br+ Ry(2hv/cm-1):

79610(16.9.16)

78370(12.9.16)

77165(15.9.16)

75905(14.9.16)

72977(7.9.16)

68684(14.9.16)67273 (13.9.16)66019 (6.9.16)

CH3+

+ Br-

Fig. 2m

The KER of 2h = 79610 show two major contributions according to the two different ion formation mechanisms (i) and (ii) (see (1); conclusion above) (ii) broad „underlying“ continuum feature corresponding to 2hr (ii) and (i) sharp peak on top.(Need to figure out what transition the sharp peak corresponds to)

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160921-CH3Br(3).pptx ; slides 38-40Likely formation mechanisms corresponding to 2hr (ii) are: a) (2hr + 1hpd) to form CH3 + Br**(Rydberg states) followed by 1hi for Br**,

which requires 4 photons in total, (fewest number of h; MOST LIKELY)b) (2hr,pd) to form CH3 + Br/Br* followed by 3hi of Br/Br*, which requires 5

photons in total OR

12

c) (2hr + 1hpd) to form CH3** + Br/Br* followed by 3hi of Br/ Br*, which requires 6 photons in total.

CH3 + Br*

CH3 + Br

b)

a & c) CH3** + Br*CH3** + Br

CH3** + Br**

CH3 + Br+/4 hv total

(CH3** + Br+/6hv total)

CH3 + Br+/5 hv total

b)

CH3 + Br**(Ry)

2hrion formationmechanisms

(CH3 + Br+/4hv total)

a) c)

Fig. 2n

Clear two components, 1) low KER and 2) high KER are observed in the 2h = 77165, 78339 and 79610 cm-1 (see Fig.2m). Most likely the low KER component is the ion formation channel (a) (Fig. 2n) whereas the high energy KER component is the ion formation channel (b) (Arnar will check)https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160908-CH3Br(2).pptx; slide 115:

1.0

0.8

0.6

0.4

0.2

0.0

2.52.01.51.00.50.0

Ry(2hv/cm-1):77165(15.9.16)

CH3+

+ Br-

eV

(a)2hr+1hpd

(b)2hr,pd

Ca. Threshold for (b)(?):Ca. Thresholdfor (a)(?):

Fig. 2p

3) Results:

13

VMI-REMPI data were collected for one color excitation corresponding to two-photon excitation to number of Rydberg states within the range of 66000 – 80000 cm-1

and electron detection, for ten wavenumber values in total:https ://notendur.hi.is/~ agust/rannsoknir/Crete16/XLS-160912.xlsx ; sheet: „Waves“:

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx ; slide 19:

80000780007600074000720007000068000660002h / [cm-1]

[3/2]np;w

[1/2]np;w

[3/2]nd;w

[1/2]nd;w

5 6 70 0 02

n =

w =5 602

02

0

02

02

02

02

4 6

4 5

3 2 1 3 2

3 2

3 2 1

3 2

6601

9

6868

4

6846

1

7265

5

7297

7

7541

875

686

7590

5

7822

5

7837

0

7819

3

7840

1

7961

0

8064

080

758

8067

4

8088

1

6650

3

6727

5

6888

2

6994

7

7424

9

7668

977

165

Fig. 3a

PES spectra were derived from the images:PES spectra: See processed data: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-161014-CH3Br(4).pptx slides: 6-7See assignments/PES spectra predictions: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-161014-CH3Br(4).pptx (AK & AH)Slides: 10-13 ANDhttps://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-161026-CH3Br(4).pptx (AH)Slides: 2-4 ANDhttps://notendur.hi.is/~agust/rannsoknir/Crete16/WORD-161017PG.docx (Pavle)Conclusions:

14

Since CH3+

are the major ions formed the major contribution to the PES´s also are linked to the CH3

+ formation, i.e. due to the two major mechanisms:2hr(ii) (2hr + 1hpd): CH3** + 1h -> CH3

+ + e-

1h(i) (i.e. 1hpd): CH3 + 3h -> CH3+ + e-

Since the former mechanism (ii) involves one-photon ionization and the latter mechanism (i) involves three-photon ionization it is convenient to compare the PES´s by h (ii) and 3h shifts (i), respectively (see (2) above).NB: The latter mechanism (i) is only significant for the 2h = 77165 and 79610 cm-1 spectra (i.e. where significant sharp peaks in the one-color KERs are observed (see (2) above)

2hr(ii) (2hr + 1hpd) mechanism (comparison of PES´s´for 1*h shifts):https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-161014-CH3Br(4).pptx ; slide: 16:

8

6

4

2

0

6420

5p (3/2)

5p (3/2)

5p (3/2)

4d (3/2)

5p (1/2)

4d (3/2)

6p; 5d (3/2)4d (1/2)

6p (1/2)5d (3/2)

6p (3/2)

7p (3/2)

1 hv

CH3(3p2A2)CH3(3d2E,3d2A1)CH3(4p2A2)CH3(4f2E)

h eV

CH3++Br-

Fig. 3bshows,: a) -(reasonably) good match of peaks corresponding to ionization (thresholds) of the i) CH3**(3p2A2), ii) CH3**(3d2E) and/or CH3**(3d2A1), iii) CH3**(4p2A2) and iv) CH3**(4f2E) for all PES´s b) –peaks corresponding to CH3** = CH3**(3p2A2) only for the four lowest energy excitation spectra (66019, 66503, 67275 and 68684 cm-1)

2hr(ii) (2hr + 1hpd) mechanism (comparison of PES´s´for 1*h shifts): The four lowest energy excitation spectra (66019, 66503, 67275 and 68684 cm-1), corresponding to resonance transitions to CH3Br**(5p) Rydberg states show transitions for v´= -1, 0 and +1:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-161026-CH3Br(4).pptx; slide 2:

15

1.0

0.8

0.6

0.4

0.2

0.0

Inte

nsity

/ a.

u.

2.52.01.51.00.50.0KER (eV)

CH3*(0,0,0,0)

CH3+(0,1,0,0) + e-

CH3*(0,0,0,0)

CH3+(0,0,1,0) + e-

CH3*(0,0,0,0)

CH3+(0,0,0,0) + e-

CH3*(1,0,0,0)

CH3+(0,0,0,0) + e-

From NIST values for CH3(3p2A2) and CH3

+(X):(1, 2, 3, 4)

CH3*(0,0,0,0)

CH3+(0,0,3,0) + e-

CH3*(0,0,0,0)

CH3+(0,1,3,0) + e-

Electron KER for 68684 (291.231nm) v = 0

v = -1

v = 1

CH3*(0,0,0,0)

CH3+(0,0,2,0) + e-

CH3*(0,0,0,0)

CH3+(0,1,2,0) + e-

v = 2

v = 3

(be, str, str, be)

Fig. 3c

1h (i) (1hpd) mechanism:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-161014-CH3Br(4).pptx ; slides: 16-18:The highest energy structure in the PES spectrum for 2h = 77165 cm-1 (see Fig. 3b above) matches thresholds for thee-photon excitation of CH3(v1,v2,v3,v4), i.e. forCH3(v1,v2,v3,v4) + 3h -> CH3

+( v1,v2,v3,v4) + e-

1.0

0.8

0.6

0.4

0.2

0.0

6420 eV

Red lines indicate 3 hvtransitions between vibrational states of the CH3 fragment

Forming CH3 in ground stateThen 3 hv photon ionization

PES for 77165 cm-1

16

0.6

0.5

0.4

0.3

0.2

0.1

0.0

5.04.84.64.44.24.0 eV

CH3

(1,0

,0,0

) + 3

h ->

CH 3+ (

0,0,

0,0)

+ e

-

CH3

(0,0

,0,0

) + 3

h ->

CH 3+ (

0,0,

0,0)

+ e

-(n0

)

CH3

(0,0

,0,1

) + 3

h ->

CH 3+ (

0,0,

0,1)

+ e

-(de

f.)CH

3(0

,0,1

,0) +

3h

-> C

H 3+ (0,

0,1,

0) +

e-

(CH

str.)

CH3

(0,1

,0,0

) + 3

h ->

CH 3+ (

0,1,

0,0)

+ e

-; O

PLA

CH3

(0,2

,0,0

) + 3

h ->

CH 3+ (

0,2,

0,0)

+ e

-; O

PLA

CH3

(0,3

,0,0

) + 3

h ->

CH 3+ (

0,3,

0,0)

+ e

-; O

PLA

CH3

(0,4

,0,0

) + 3

h ->

CH 3+ (

0,4,

0,0)

+ e

-; O

PLA

CH3

(0,5

,0,0

) + 3

h ->

CH 3+ (

0,5,

0,0)

+ e

-; O

PLA

Possible PES´s due to CH2** + 1h -> CH2+ + e-:

Thresholds corresponding to one-photon ionization of CH2**suggest that “the low energy side” of a broad peak at about 1.7 eV on a 1hv shift scale shown below is due to CH2**(3p) + 1h -> CH2

+ + e-:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-161014-CH3Br(4).pptx ; slides: 12:

8

6

4

2

0

43210

66019

66503

67275

68684

72977

74249

77165

75905

78339

79610

5p (3/2)

5p (3/2)

5p (3/2)

4d (3/2)

5p (1/2)

4d (3/2)

6p; 5d (3/2)4d (1/2)

6p (1/2)5d (3/2)

6p (3/2)

7p (3/2)

1 hv

CH2(3p) CH2(3d3A2)(C)(D) CH2(4p)

17

Yet unassigned features in the PES´s could be due to various other ionization channels, such as:CH3 + 2h -> CH3

+ + e- (low energy)CH2** ->->-> CH2

+ + e-

CH/CH** ->->-> CH+ + e-

Br/Br*/Br** ->->-> Br+ + e-

CBr** -> CBr+ + e-

18

4) Results: VMI-REMPI data were collected for two color excitation corresponding to two-

photon excitation to number of Rydberg states within the range of 66000 – 80000 cm-1 and Br and Br* detection -, for five wavenumber values in total:https ://notendur.hi.is/~ agust/rannsoknir/Crete16/XLS-160912.xlsx ; sheet: „Waves“:

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx ; slide 18:

80000780007600074000720007000068000660002h / [cm-1]

[3/2]np;w

[1/2]np;w

[3/2]nd;w

[1/2]nd;w

5 6 70 0 02

n =

w =5 602

02

0

02

02

02

02

4 6

4 5

3 2 1 3 2

3 2

3 2 1

3 2

6601

9

6868

4

6846

1

7265

5

7297

7

7541

875

686

7590

5

7822

5

7837

0

7819

3

7840

1

7961

0

8064

080

758

8067

4

8088

1

6650

3

6727

5

6888

2

6994

7

7424

9

7668

977

165

Fig. 4a

KER spectra and angular distributions were derived from the images:KER spectra: See processed data: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160921-CH3Br(3).pptx; slides 2 -42See assignments/KER spectra predictions: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160928-CH3Br(3).pptxAngular distributions: https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160921-CH3Br(3).pptx; slides 43-56

19

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx , slides 38-39:Br and Br* atoms were detected by (2r +1i) REMPI for the resonance transitions:Br ->-> Br**(4P3/2); excitation = 266.6784 nm / 2h= 74996.6720 cm-1.Br* ->-> Br**(2D3/2); excitation = 266.7420 nm / 2h= 74978.8185cm-1.These excitations correspond to ion formation according to the 1h (i) mechanism (see above)

77000760007500074000730002h / [cm-1]

BrBr**(4P3/2)

Br*Br**(2D3/2)

[3/2]nd;w

3 2 [1/2]nd;w

[3/2]np;w

[1/2]np;w

Dye lasers / probe transitions

75009.1374991.41

Fig. 4b Images / spectra were recorded,

a) –for both laser radiations; probe laser (Dye laser) delayed by about 10 ns with respect to the pump laser (MOPO) beam, i.e. “two-color data”.b) -for pump laser (MOPO) onlyc) –for probe laser (Dye laser) onlyTypical results were as the following (for 2h = 67275 cm-1):see https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160921-CH3Br(3).pptx, slide 11:

1.0

0.8

0.6

0.4

0.2

0.0

1.00.80.60.40.20.0

KERs (xx) / Br (533.358nm) detect.:

Ry(2hv/cm-1):67275(21.9.16)

eV

FromMOPO

FromDye laser

Both lasers

Fig. 4c

20

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160921-CH3Br(3).pptx , slide 41-43:Thus the “two-color KERs” are typically found to be made of three major components:a) medium KERs with a sharp peak, b) broad high KERs and c) broad low KERs:a) The medium KERs (a) correspond to ion formation mechanism 1h(i) (which gives sharp peaks) primarily due to the probe / dye laser, i.e.1hpd of CH3Br by the probe radiation to form CH3 + Br/Br* followed by the (2r+1i)REMPI (probe) of Br/Br*b) The broad high KERs correspond to ion formation mechanism 2hr(ii) (which gives broad peaks) by the pump and probe radiations, i.e.2hr,pd of CH3Br by the probe radiation to form CH3 + Br/Br* followed by the (2r+1i)REMPI (probe) of Br/Br*c) The broad low KERs correspond to ion formation mechanism 2hr(ii) (which gives broad peaks) by the pump and probe radiations, i.e.(2hr + 1hpd) of CH3Br by the probe radiation to form CH3** + Br/Br* followed by the (2r+1i)REMPI (probe) of Br/Br*:

CH3 + Br

a)

c) CH3* + Br

c)

CH3* + Br+/6hv total

CH3 + Br+/4-5 hv total

a-b)

CH3 + Br**

CH3* + Br**

b)

Fig. 4d

21

1.2

1.0

0.8

0.6

0.4

0.2

0.0

1.00.80.60.40.20.0

(b)(c) (a)

eV

Ry(2hv/cm-1):72977(21.9.16)

2hr,pd

1hpd2hr+1hpd

Fig. 4e

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160921-CH3Br(3).pptx , slide 31:Relevent thresholds corresponding to mechanisms (b) and (c) above are shown below:b): for CH3 + Br formation after 2hr,pd (for 2h = 66019, 67275 and 72977 cm-1)c): for CH3**(3p2A2) + Br formation after 2hr + 1hpd (2hr = 66019, 67275 and 68684 cm-1)c) for CH3**(3d) + Br formation after 2hr + 1hpd (2hr = 72977 cm-1)

1.0

0.8

0.6

0.4

0.2

0.0

1.00.80.60.40.20.0

KERs (xx) / Br (533.358nm) detect.:

eV

Both lasers„Total signal“

Ry(2hv/cm-1):75905(22.9.16)72977(21.9.16)68684(22.9.16)67275(21.9.16)66019(21.9.16)

Normalizationpoints

Thresholds for CH3+Brformation after 2hr

Thresholds for CH3**+Brformation after 2hr + 1hpd

Fig. 4f

The angular distributions for (c)/”low KERs”/Br*(Br) detection, according to the two-color detection and the CH3**(3p2A2) formation according to one-color detection (see above, Fig. 2j) are found to be comparable. This suggest a common formation channel

22

of 2hr+1hpd followed by a formation of CH3**(3p2A2) + Br*(Br): https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160921-CH3Br(3).pptx, slide 57:

2

Low KER

High KER

Medium KERTwo color,

Br* detectionBr detection

Summary2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

74727068x103

Fig. 4gVS.

2.0

1.5

1.0

0.5

0.0

-0.5

-1.0

78767472706866x103

2

1.2932 660190.71411 665031.1593 672750.71876 686842.0226 729771.3393 74249-0.058 759050.5568 771650.2957 783700.0092239 79610

CH3+

23

5) Results: VMI-REMPI data were collected for two color excitation corresponding to two-

photon excitation to a Rydberg state within the range of 66000 – 80000 cm-1 and CH3

detection -, for one wavenumber value (one Rydberg state) (72977 cm-1) :

https ://notendur.hi.is/~ agust/rannsoknir/Crete16/XLS-160912.xlsx ; sheet: „Waves“:

https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-160904-CH3Br(1).pptx ; slide 20:

80000780007600074000720007000068000660002h / [cm-1]

[3/2]np;w

[1/2]np;w

[3/2]nd;w

[1/2]nd;w

5 6 70 0 02

n =

w =5 602

02

0

02

02

02

02

4 6

4 5

3 2 1 3 2

3 2

3 2 1

3 2

6601

9

6868

4

6846

1

7265

5

7297

7

7541

875

686

7590

5

7822

5

7837

0

7819

3

7840

1

7961

0

8064

080

758

8067

4

8088

1

6650

3

6727

5

6888

2

6994

7

7424

9

7668

977

165

KER spectra were derived from the images:KER spectra:https://notendur.hi.is/~agust/rannsoknir/Crete16/PPT-161116-CH3Br(5).pptxSlides 2, 4-6,

24