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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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How to recreate bioluminescence in fireflies in a lab?

I have several mg/mL of D-luciferin, luciferase (firefly), ATP solution (25 mmol) and MgSO4 (for the mg2+ ions). The experiment has to be done in cuvettes of 2,5 mL (if I get any results, it will be ...
7
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1answer
68 views

What could cause a peak to split into 2 resonances as temperature increases in NMR spectroscopy

I understand that some peaks may coalesce upon an increase in temperature due to an increase in free rotation, this does occur with some peaks in my data. Why might you see a peak split into two other ...
7
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1answer
46 views

How to determine the number of water ligands attached to Pd in palladium chloride aquacomplex PdClₓ · yH₂O?

Normally this can be achieved using UV-vis: there is a strong absorbance around wavelength 220 nm which varies based on the number of ligands. If the palladium concentration is too high, the solution ...
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1answer
50 views

What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state?

When an electron in a higher energy state jumps to a lower energy state in Bohr’s model of hydrogen atom, it emits a photon which has energy equal to the difference in the energy between the final and ...
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38 views

Internal standard with low T1 for NMR quantification of ammonia

I am trying to quantify low levels of ammonia with NMR. The good news is that ammonia has a very low T1 (<0.5) which shortens d1 a lot. However, I cannot find any internal standard with a T1 that ...
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1answer
36 views

Spin-forbidden transition iof bromine

In one of the lectures of my spectroscopy course, the professor claimed that there is a strong absorption band in the UV/Vis spectrum of bromine, associated with a singlet-state to triplet-state ...
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0answers
19 views

why do cone cells have broad responsivity spectra peaks?

My understanding of vision is that, although the cone cells in our eyes can detect three colors, there is enough overlap in the responsivity spectra (as shown here: https://en.wikipedia.org/wiki/...
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1answer
24 views

Absorbance maxima of polyenes [closed]

Can anyone tell me how to approach this question from USNCO 2013?
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0answers
25 views

How do we determine the proportions of hydrogen to helium (to other elements) that make up the Sun given the absorption spectra?

I am reading about the composition of the Sun and how it is made up of mostly hydrogen (~90%) and helium (>10%) and other elements with much smaller quantities. The explains that different elements ...
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2answers
71 views

Flame Test Spectrograms Not Lining Up With Reality

In my AS Level chemistry class we had tried some DIY spectroscopy of flame tests with the aim of identifying anions in certain salts. We got as far as building the spectrometer inspired by Paper Craft ...
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2answers
311 views

Relationship between the symmetry number of a molecule as used in rotational spectroscopy and point group

While doing a problem set I noticed that the symmetry number of a molecule turns out (usually) to be half the number of symmetry elements that the point group the molecule belongs to. When I say ...
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1answer
41 views

Why the chemical shift value of a proton be negative in proton NMR spectroscopy where TMS is used as standard reference?

If there's any possibility of chemical shift value of a proton be negative.And if yes...why..when I am using TMS as a standard reference.
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2answers
109 views

Why doesn't the current stop in neon lamps when all the atoms have been ionized? [closed]

My personal experience (which could be wrong) tells me neon lamps can theoretically run on forever or at least a very long time. If current is the flow of charge why doesn't it stop once all the atoms ...
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3answers
96 views

Heisenberg uncertainty principle and lifetime of the excited state

A key relation in optical spectroscopy also used to derive natural bandwidth is: $\Delta E \Delta t=ℏ$ $\Delta E$ is the energy uncertainty of a state, $\Delta t$ should be the uncertainty of the ...
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1answer
28 views

How to measure UV index? [closed]

I am a high school student so please apologise if I say something very dumb or irrelevant. I am conducting an experiment in which I want to find UV index at different points. Such as under shade, ...
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37 views

Is it true that “Voigt Circuit” would be able to be fitted to various electrochemical impedance spectra?

"Voigt Circuit" which is a series combination of Voigt elements (i.e. parallel RC's), is commonly used for Kramers-Kronig relations checking; and as I imagine it is generally believed to be able to be ...
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1answer
64 views

Formulas for the number of spectral lines

While reading through Narendra Avasthi's Problems in Physical Chemistry, I came across two formulas on p. 64 (Scanned page): When electrons de-excite from higher energy level ($n_2$) to lower ...
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1answer
144 views

Raman transition and IR transition

In a character table one can find the reducible representation of vibration of a molecule. In such a table we also see things like $xy,z,x...$. If this corresponds with an irrep we say that IR ...
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17 views

What band of IR would be reflected by vegatable oil?

I am trying to select a lidar sensor for measuring the distance through air to vegetable oil. My current sensor emits 850nm infrared light, however, it sees through the vegetable oil quite well (as ...
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1answer
26 views

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 ($\ce{O+}$...
9
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2answers
61 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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1answer
14 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 ...
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1answer
69 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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2answers
57 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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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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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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0answers
20 views

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
36 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
34 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
28 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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2answers
59 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
59 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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77 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 ...
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2answers
92 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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1answer
71 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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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
116 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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105 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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62 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
58 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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68 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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58 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
152 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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51 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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56 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 ...
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1answer
433 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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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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1answer
321 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 ...