Eirík´s project(?) CH 3 I: agust,www,...rempi/ch3i/PPT ak.ppt ( ) agust,heima,...REMPI/CH3I/PXP ak.pxp (energetics and abs. spectrum) (energetics) 1)compound: availability and physical properties 2)Absorption spectra on www 3)Papers 4)Energetics(?)

Eiríks project 1) CH 3 I: Svana´s , :

: liquid Vapor pressure: CRC: 1 mm mp S-45.8oC Vapor pressure = 100 Torr for -7 o C See cooling baths:

ATH 1 ATH 2

agust,heima,...REMPI/CH3I/PXP ak.pxp; Lay:0, Gr:0 ATH 1 (2007)

agust,heima,...REMPI/CH3I/PXP ak.pxp; Lay:0, Gr:0 ATH 1

ATH 2 agust,heima,...REMPI/CH3I/PXP aka.pxp; Lay:0, Gr:0

Absorption references:

Absorption references:

Absorption references: See tables 4-7 in The paper

Check REMPI work -by Donovan et al. -references in CH3Br REMPI paper etc. With repect to Rydberg state structure.

Papers: See also Eirik´s folder Rydberg states: RESONANCE-ENHANCED MULTIPHOTON IONIZATION PHOTOELECTRON- SPECTROSCOPY ON NANOSECOND AND PICOSECOND TIME SCALES OF RYDBERG STATES OF METHYL-IODIDE Abstract: Rydberg states of methyl iodide have been investigated using resonance enhanced multiphoton ionization in combination with photoelectron spectroscopy with nanosecond and picosecond laser pulses. The study of the ns (6 less-than-or-equal-to n less-than-or-equal-to 10) Rydberg states in two-, three-, and four-photon excitations has resulted in an unambiguous identification of state [1] in the 7s and 8s Rydberg states. As a consequence, it is concluded that the transition to 6s[1] in two- and three-photon excitations is anomalously weak. The application of photoelectron spectroscopy to identify the electronic and vibrational nature of a resonance has led to a major reinterpretation of the excitation spectrum of the 6p Rydberg state in two-photon excitation. In many of the recorded photoelectron spectra anomalous electrons are observed, which derive from a one-photon ionization process. This process is suggested to find its origin in the mixing of 6p and 7s character into higher-lying Rydberg states. The major difference between resonance enhanced multiphoton ionization photoelectron spectroscopy with nanosecond and picosecond lasers is found in a less effective dissociation of the molecule in the picosecond experiments....Ry states, state mixing, vibr. Freq. Modes, (2+1)REMPI spectra and assignments of Rydb. states

(2+1)REMPI..3p Ry

Shows 1) mass spectra and 2) energetics

Bond energies,..

1) Isotopic effect in the (2+1) REMPI spectra of (13)C-substituted methyl iodide for UV selective dissociation To investigate a possible means of achieving isotopic enrichment of methyl iodide (CH(3)I), we studied the 6s Rydberg states of (13,12)CH(3)I by (2+1) resonance-enhanced multiphoton ionization. For 3; 3(1)(0) band (v3 hot band) excitation ( at a full width at half maximum of 14 cm (1)), we observed a well-resolved isotope shift of +16 cm (1). The band shape, which has a broad shoulder on the red side and an abrupt decrease on the blue side, indicates that this resonance is ideal for enriching the concentration of the desired lighter isotope (the isotopomer). (C) 2011 Elsevier B.V. All rights reserved. 2) Photoelectron imaging of 8p Rydberg states of atomic iodine following methyl iodide A-band decomposition Photoelectron imaging technique has been applied to study (2 + 1) REMPI of atomic iodine through 8p Rydberg states around 253 nm. Full three-dimensional state-specific speed and angular distributions of the photoelectrons were recorded. The branching ratios among the different I(+) levels revealed that the perturbation on ((3)P(2))8p series is particularly large among the ((3)P(2))np series. The violation of core-conserving ionization is attributed to the interactions between the ((3)P(2))8p and ((1)D(2))6p series. The photoelectron angular distributions were found to be well characterized by P(2)(cos theta) and P(4)(cos theta). A relatively high positive beta(2) and a relatively low beta(4) observed in (2 + 1) REMPI process indicated that the ionization process can be approximately considered as single-photon ionization via the weakly aligned ((3)P(2))8P intermediate states. (C) 2009 Elsevier Inc. All rights reserved. Less useful but new papers:

Now we need to look at the energetics, analogous to that for CH2Br2: (See slides 6 -11)

Fig 10:

NIST IE: cm-1

cm-1

CH3:

CH3I D: 2.38eVhttp:// Factors: f1:8.36E+01cm-1 / (kJ mol-1) f2:3.50E+02cm-1 / (kcal mol-1) f3: cm-1/eV E(6s) = cm-1E(4P;5s)+D= cm-1 IE(CH 3 I)=9.54eVNIST IE(CH 3 I)= cm-1 IE(I)= cm-1http://physics.nist.gov/cgi-bin/ASD/energy1.pl E(S/O;I)= cm-1http://physics.nist.gov/cgi-bin/ASD/energy1.pl E(CH 3 +I*(1/2))= cm-1 E(CH 3 +I + + e)= cm-1 IE(CH 3 ) =9.84eV cm-1 NIST E(CH e + I) cm-1 EA(I) = eVhttp://en.wikipedia.org/wiki/Electron_affinity_%28data_page% cm-1 E(CH I-)= cm-1 E(I + )-E(I*)= cm-1

CH 3 + I; CH 3 + I*; CH 3 + I**(min); CH e + I; CH 3 + I + + e; CH 3 I CH 3 I + + e; cm -1

CH 3 + I; CH 3 + I*; CH 3 + I**(min); CH e + I; CH 3 + I + + e; CH 3 I CH 3 I + + e; Abs. spectrum (1) (2) (3) (4) (n) = number of photons

CH e + I; cm-1..threshold hv(Laser)= ( nm) CH 3 + I + + e; cm-1..threshold: hv(Laser) = ( nm) cm -1

REMPI spectra and assignments from the literature:

n: n: s -States and spectra observed in Two-photon REMPI n = number of resonance excitation photons

n: n: s -States and spectra observed in Two-photon REMPI

n: n: s -States and spectra observed in Two-photon REMPI

: hv p -States and spectra observed in Two-photon REMPI

p states spectra observed in (2+n) REMPI s states spectra observed in (2+n) REMPI Ca. Spectral region for R590!

p states spectra observed in (2+n) REMPI s states spectra observed in (2+n) REMPI

p states spectra observed in (2+n) REMPI Comparison of absorption and REMPI spectra:

CH 3 + I; CH 3 + I*; CH 3 + I**(min); CH e + I; CH 3 + I + + e; CH 3 I CH 3 I + + e; Abs. spectrum (1) (2) (3) (4) (n) = number of photons x100 The A-band

CH 3 I + + e; Abs. spectrum (1) (2) (n) = number of photons x100 The A-band n  *(C-I) cm-1) cm-1

CH3+ 1D REMPI uncorrected Absorption spectrum 2hv

??? cm -1 pnt

IDEA!: an I 2 + mass peak observed could be due to a molecular dimer (CH 3 I) 2 ERGO: let´s see the effect of less cooling, i.e. 1)less % argon 2) less backing pressure. Let´s check the literature Literature: 1) : Van der Waals complexeshttp:// 2) : “Ground electronic state I 2 is formed from the photolysis of methyl iodide dimers” 3)Sjá meira neðar See example for effect of buffer gas (rare gas) on jet cooling next slide:

Largest molecular density= molecular beam Small molecular density= molecular diffusion medium molecular density Skimmer; Not used in our case Beam axis :

:

: & :

1 mm PTorr S t/oC T/K /T (K-1) ln(p) 1/T (K-1) /T (K-1) Ln(p) ln(p) vs 1/T is nonlinear suggesting less importance of dimers as temperature rizes.

This could mean that CH 3 I dimers are even formed in the vapour above the trap when cooled with CCl 4 slash bath (-23 o C)!! --further suggesting that it might be better to use less cooling for the trap: How about to use cold water only (analogous to that used for CH 2 Br 2 earlier) ???

CH3+ 1D REMPI uncorrected Absorption spectrum 2hv No clear correspondance between REMPI and absorption spectra in this region

CH3+ 1D REMPI uncorrected Absorption spectrum 2hv What on earth is that???

CH3+ 1D REMPI uncorrected Absorption spectrum 2hv This looks like P, Q and R brances Of symmetric top: seen next slide  =

IR róf topsamhverfra sameinda / IR spectra for symmetric top molecules: CH 3 I: Topsamhv. B: Fundamentals of Molecular Spectroscopy eftir C.N. Banwell og E.M. McCash, (McGraw-Hill, 4. útg. 1994)

Are these all iodine atomic lines? What transitions are these, Eiríkur? hv(laser)

Same molecular peak seen in the I+ and CH3+ spectra hv(laser) C atomic lines Small but significant peak

og cm-1 ftp:// /Data/CH3I/Calibartion Work/calibration/ allt I cal, 16220_17510 funky17540_ pxp allt I cal, 16220_17510 funky17540_ pxp CH3+ REMPI

cm-1 og ftp:// /Data/CH3I/Calibartion Work/calibration/ allt I cal, 16220_17510 funky17540_ pxp allt I cal, 16220_17510 funky17540_ pxp cm CH3+ REMPI

og ftp:// /Data/CH3I/Calibartion Work/calibration/ allt I cal, 16220_17510 funky17540_ pxp allt I cal, 16220_17510 funky17540_ pxp I+ REMPI

Symmetric top:

cm-1 OUR CH3+ REMPI spectrum At is Due to CH3 !!!! Check this reference

:

: cm-1 Ours NB!:  K = 0

: Ground state Excited state Coupling terms NB!:  K = 0

..but what about this spectrum: It must be because of CH3 There is no reported electronic state for CH3 at this wavenumber The spacing of cm-1 between the two CH3+ spectra suggests that it could be A vibrationally excited state cm cm-1

Could be the a2 2 (OPLA) vibrational mode Let´s check references out ‐ of ‐ plane large amplitude (OPLA)-mode = umbrella modes

NB!: OPLA modes can be significantly different for excitede states than for The ground state, thus: NIST: these seem, generally to be the lowest numbers

O PQ R S Our spectrum simulated for parameters in : Calculations were performed in cm-1

Since the Q branch in the cm -1 system is degraded to red (low wavenumber) opposide of what is found for the cm -1 system (slide 72) it suggest that B´< B´´ opposide of what is found for the cm -1 sysem (see slide 68) where B´= 9.90 cm -1 and B” = cm cm -1 First attempts to simulate the vibrationally excited band of CH3:

= B” =D N ” =D NK ” 9 =B´ =D N ´ =D NK ´ “= =  C 0 =  DK R Q S P O  K = cm -1