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Questions tagged [spectroscopy]

Use this tag for questions about spectroscopic methods in practice and in theory, especially where more specific tags for the individual method (such as [tag:nmr-spectroscopy] or [tag:ir-spectroscopy]) are not available.

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Potential energy curve for dissociation of cation of carbon dioxide

Can anyone suggest me some literature where I can find the potential energy curve or the electronic states for singly ionized $\ce{CO2}$ ($\ce{CO2+}$) dissociating into singly charged oxygen ($\ce{O+}$...
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2answers
55 views

High content of potassium reported by spectrometer in silverware items

We tried to analyze a few silver items (800/1000 fineness) using a hand-held ED-XRF spectrometer, which is normally used for analyzing industrial alloys etc. The operating element range of the device ...
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11 views

Does the magnetic quantum number selection rule influence the atomic emission spectrum [closed]

When drawing emission line spectrum does the selection rule which involves the magnetic quantum number influence the transitions?
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34 views

Are there IR spectras to exercise [duplicate]

I was wondering if there is a place I could exercise on IR spectras with explanations given on them. If this is a stupid question or if it is asked in the wrong place, please downvote me to hell. ...
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0answers
29 views

Spectroscopy in organic chemistry [duplicate]

I'm sorry if I am posting in the wrong place, I just wanted to ask what are the best textbooks to learn spectroscopy used in organic chemistry ( IR, MS, NMR etc.). Thanks alot in advance!
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1answer
13 views

Taking a procedure for ICP and adapting it to use with AAS

I was reading a paper regarding metal detection and they gave their procedure for an acid digest of a soil sample which was then analysed by ICP-OES. They used nitric acid, hydrogen peroxide and ...
4
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1answer
53 views

The carbon-13 NMR for 1,1,1-trichloroethane

I was working the following spectroscopy problem from Clayden 2e that asks us to identify the structure of a compound from information about its carbon-13 NMR peaks. Problem 3.5: The solvent ...
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0answers
20 views

Raman spectrum of acid acetic with deuterium?

I have raman spectrums of 3 differents acetic acid in solution : $$CH_3COOH \qquad \qquad CH_3COOD \qquad \qquad CD_3COOD$$ All the following are hypothesis from me and I would like to know if it's ...
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2answers
44 views

Do microwaves heat polar molecules or molecules with polar bonds?

IR is only absorbed my molecules with polar bonds regardless of the overall polarity of the molecule , what about Microwaves ?
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1answer
21 views

Can nuclear shielding affect relaxation time?

Can nuclear shielding affect the transverse relaxation time, i.e extend the relaxation time the more the nuclei is shielded?
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21 views

Are there any selection rules for collisional excitation/relaxation?

There are well-known selection rules for possible optical transitions of an isolated atom (molecule) between different electronic states. But are there any rules, limiting possibilities of collisional ...
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0answers
22 views

Does conjugation increase λmax of n to π* transitions as well as π to π* transitions?

I would presume yes if the lone pair is on an atom involved in the conjugated system, but no if the lone pair is not on an atom involved in the conjugated system.
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0answers
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Molar extinction coefficient a measure of the probability of a photon of the associated wavelength being absorbed?

Obviously the molar extinction coefficient is not equal to the probability of a photon of the associated wavelength being absorbed, but is it a measure of the probability i.e. the higher the value of ...
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Are the molar extinction coefficient and cross-section of an absorption related to the probability of absorption?

I have struggled to find a formal definition of cross-section of absorption; from what I've gathered, its best defined as 'the intensity of absorption'. Wikipedia's formal definition of the molar ...
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1answer
30 views

UV Absorption of iodine with some solvent

$I_2$ in solution is typically absorbing around $525 \; nm$ this is why it appear to be magenta, I recently learn that with some solvent : Benzene Toluene $o$-Xylene $p$-Xylene The coordination ...
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1answer
30 views

Is a time domain spectrum obtainable from a frequency domain spectrum? [closed]

I know for a fact that a frequency domain spectrum can be obtained from a time domain spectrum using a Fourier transform - but can you do the reverse? Also what are the advantages and disadvantages ...
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1answer
26 views

Are we using an assumption in calculating the ratio of first state excited to unexcited chemical species using the Boltmann distribution?

In calculating the ratio of first state excited to unexcited chemical species using the Boltzmann distribution, are we assuming that we only have species in the unexcited and first state excited ...
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1answer
32 views

Angle of Light Source for Absorbance Spectroscopy

I apologize if this question is stupid, but have been puzzled by it for a few days. Say I have a spectrometer measuring in the visible light range and we're looking to measure the absorbance on a ...
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0answers
24 views

How to use Hund third rule for cases like Nb, Ru, Rh, Pt?

How do I use Hund third rule to determine the value of $J$ for ground state for cases like Nb, Ru, Rh, Pt where there is 1 electron in s orbital and then an incomplete p orbital, and besides, S nor L ...
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2answers
57 views

Restrictions on transitions in Spectroscopy

Just for the sake of an example, let's assume a transition from one energy state to a higher energy state in atomic absorption spectrum If the energy difference between the ground state and first ...
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0answers
37 views

Spectral database in the UV-Vis/NIR and IR regime

I'm searching for a bunch of spectra (some tens), preferably with intense bands in the Vis spectrum, to play around with (calculating chromaticity, etc.). They should range from 250 nm to 2500 nm (UV-...
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0answers
59 views

Determining absorption spectrum, magnitude of Δo and spin for Iron Oxalate

Iron Oxalate ions form an emerald green solution when dissolved. If the ions in solution appears emerald green to our eyes, what color of visible light is it mostly absorbing? What does that tell you ...
4
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2answers
90 views

Is there a finite number to the possible state of electron in an atom?

Okay, I know you may say, there are infinite numbers of possible state of an electron between its ground state and ionic state, since energy levels get continuous as electron gets farther away from ...
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58 views

PLQY for FIrpic, Rhodamine 6G, Ir(ppy)3, and 4CzIPN?

I'm looking for PLQY values for FIrpic, Rhodamine 6G, Ir(ppy)3, and 4CzIPN in solution, or in thin film (preferrably). Is there anyone who knows those values from reliable source?
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1answer
69 views

Franck-Condon factors in photoelectron spectroscopy

Franck-Condon factors have been used to predict / assign the vibrational structure of photo-electron spectra. $FCF=|\langle\psi''_{vib}|\psi'_{vib}\rangle|^2 = |\langle\psi''_{vib,1}\psi''_{vib,2},\...
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0answers
77 views

Why is spin-contamination undesirable?

Why is spin-contamination, introduced by e.g. Unrestricted Hartree Fock, undesirable, and to which problems further on can it lead? The only problem I currently see myself is that spin-contamined ...
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1answer
115 views

Do molecules change shape when they become vibrationally excited?

In quantum mechanics we learn the the classical picture of a vibrational excitation is wrong. The atoms will 'vibrate' only while the molecule is in a coherent superposition of two vibrational states, ...
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29 views

What is the lambda max of formaldehyde?

I am working with a remote sensing spectroscopy unit and attempting to measure formaldehyde vertical column densities in the atmosphere. The instrument's fitting window needs to be set to the lambda ...
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0answers
98 views

Vibrational Self-Consistent Field

There are a few things about VSCF that I don't understand: Which coordinates do you work in? If you work in normal mode coordinates, how do you evaluate the effect of the average of one normal mode ...
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0answers
49 views

Evaluating Franck-Condon factors

Franck-Condon overlap integrals are given by $\langle\psi^e_{v_e}|\psi^g_{v_g}\rangle$, where $\psi^e_{v_e}$ and $\psi^g_{v_g}$ are the vibrational functions for the $v^{th}$ vibrational states of the ...
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1answer
52 views

What is the relationship between emission and fluorescence?

A molecule exposed to a photon with some energy is put into an excited state, and emits a photon of some energy when it returns to ground state. The photon that provided the energy for excitation ...
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0answers
53 views

Where can I find example MS, IR, NMR spectra for teaching molecular spectroscopy?

I am teaching a course on analytical chemistry, and I would like to give my students MS, IR and NMR spectra to practice with. It would be ideal if they could analyze spectra in a more "realistic" way ...
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0answers
35 views

Absence of anti-Stokes line in Raman spectrum

If we have a molecule 1H-25X which shows a band at $3000~\mathrm{cm}^{-1}$ in the IR spectrum and you want to record a Stokes and anti-Stokes Raman spectrum with a laser of 1000 nm, why is the anti-...
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1answer
109 views

What is the difference between X-ray photoelectron spectroscopy and X-ray absorption spectroscopy?

XPS is used for surface chemical state identification. But other than that, is XAS just an inverse of XPS?
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41 views

Why aren't lasers used as light sources for atomic absorption spectroscopy?

Atomic absorption spectroscopy yields extremely narrow signals. It is difficult to separate white light with sufficient precision using monochromators, and hollow cathode lamps are often used as light ...
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0answers
43 views

Differences between LIBS over LA-ICP-MS? [closed]

Which differences should I consider between the techniques Laser-Induced Breakdown Spectroscopy and Laser Ablation Inductively Coupled Plasma Mass Spectrometry for a geochemistry fingerprint focused ...
2
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1answer
304 views

Can visible light or infrared radiation excite electrons?

So the limit of ionizing radiation seems to be UV light. I'm wondering if IR light or Visible light can excite the electrons in an atom. It has to do with the difference in energy level right? So ...
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0answers
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How does activated carbon catalyse oxidation?

Context: I am doing an experiment on the quantitative analysis of ascorbic acid in a blackcurrent syrup using fluorescence spectroscopy. In order to do so, ascorbic acid was first oxidised into ...
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31 views

Blank in Fluorescence spectroscopy

Quantum dots were dissolved in Millipore water and used as a sensor for the determination of an analyte by fluorescence spectroscopy. I need to know what blank is in this system? Millipore water, or ...
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1answer
140 views

Why do carboxylic acid derivatives show a more upfield shift than carbonyls in 13C-NMR?

The prototypical 13C NMR shifts of carbonyl carbons is in the range 190–200 ppm, however, carboxylic acid derivatives have a 13C NMR shift in the range 160–180 ppm instead. What structural factors ...
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19 views

The Salt Effect stops working in extreme cases?

I and three friends did an experiment where we investigate the salt effect, also known as the uncommon ion effect. The specifics are that we made a $\pu{1L}$ solution saturated with $\ce{CaCO3}$ and $...
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1answer
3k views

What is number of 1H NMR signals for toluene?

I am searching the web for the number of 1H NMR signals of toluene and I find two different results. Some say there are two signals while others say there are four (According to me, it should be 4). ...
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0answers
30 views

Effect of interaction between lactic acid and glucose monohydrate on optical rotation

Would anyone know why I get double the expected optical rotation (OR) result for a solution containing D(+)-glucose and L(+)-lactic acid in comparison to a solution of D(+)-glucose on its own? When I ...
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2answers
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What is an exocyclic double bond?

I have been tasked to find the $\lambda_{\text{max}}$ of 3,4-dimethyl-1,2,3,4,4a,5-hexahydronaphthalene. This was supposed to be fairly easy. I used the base value for homoannular diene ($\pu{253 nm}$...
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0answers
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Raman database of polymer spectra for analyses in R/python

Can anyone reccomend a raman database of polymer spectra that is open source or freely available? I'm analyzing spectra of a number of plastics and looking for reference spectra for identification. ...
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1answer
46 views

How to interpret detection limits

I am learning about different analytical methods such as Atomic Absorption Spectrscopy and Atomic Emission Spectroscopy and I'm having a difficult time understand how to interpret the detection limits ...
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1answer
73 views

Detection limits

I am given this question: A study showed that over 2000 children in China have been poisoned by lead. Blood samples have been taken and show that there is 10 times as much as the acceptable amount of ...
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1answer
157 views

Stretching frequency of nitro and nitrito

I got the values of the stretching frequency of nitro and nitrito ligands from this webpage. I understand why stretching frequencies are close in nitro and well separated in nitrito. How to explain ...
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1answer
133 views

Maximum (Z) to (E) ratio in the photoisomerization of azobenzene?

Considering the photoswitching of azobenzene, I was told the following argument: Considering that the photoexcited state of azobenzene has a about 50% to 50% chance of yielding either the (E)- or (Z)-...
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1answer
85 views

Comparison of chemical shifts among alkanes in NMR spectroscopy

I was reading through the factors influencing chemical shifts in proton NMR. I found the order of chemical shifts in the image above. Why is this order supposed to be as it is? I thought it would be ...