Infrared multiple photon dissociation IRMPD

Fragmentation of peptides can also be observed with FTICR instruments. Infrared multiple photon dissociation (IRMPD) and electron capture dissociation (ECD) have been introduced as two alternative dissociation methods to the low-energy CID method. The IRMPD method produces many fragments that make the spectrum very complex and difficult to interpret. Some of the fragment types observed with IRMPD are b and y type ions or these ions that have lost ammonia or water. However, most of them are not these types of fragment ions. 

Vibrational spectroscopy is an important probe used to determine the bonding and structural properties of molecules. Powerful techniques such as electron energy loss spectroscopy (EELS) have been developed, which allow one to obtain the vibrational properties of molecules chemisorbed upon surfaces. Due to low concentration, the highly reactive nature of the clusters, and the large number of possible species which are typically present in the cluster beams used to date, unconventional techniques are required in order to obtain spectroscopic information. One unconventional but powerful technique, infrared multiple photon dissociation (IRMPD), has recently been applied to the study of the vibrational properties of gas-phase metal clusters upon which one or more molecules have been chemisorbed. This same technique, IRMPD, has previously been used to obtain the vibrational spectra of ions, species for which it is difficult to apply conventional absorption techniques. 

As mentioned earlier, CPMD simulations were carried out at 300K on deprotonated phosphorylated serine (p-ser-H) , and the resultant extracted spectrum correlates with the experimental IR spectrum obtained by the recently-developed InfraRed Multiple Photon Dissociation (IRMPD) technique, which was first described in this chapter in Volume 39. 

A wide variety of lasers have been used in combination with trapping mass spectrometers. Two lasers in particular are incorporated already into many commercial mass spectrometers the CO2 (X= 10.6 pm or 0.12 eV photon ) and nitrogen (X=337 nm or 3.68 eV photon ) lasers. The former is used for performing infrared multiple photon dissociation (IRMPD) experiments (mostly in ICR instruments, see Section 9.3) while the latter is used commonly in MALDl ionization sources. Other commonly-used lasers are Q-switched Nd YAG lasers (fundamental X= 1064 nm... 

Nucleotides are covered elsewhere in this volume but worthy of mention is the cyclic 3, 5 -adenosine monophosphate anion (cAMP-H) , generated in gaseous species by electrospray ionization (ESI) and stored in an ion-trap mass spectrometer. This has been investigated by mass-resolved infrared multiple photon dissociation (IRMPD) spectroscopy in the 900 1800 cm fingerprint range using the powerful and continuously-tunable radiation from a free electron laser. Further details of this IRMPD application are given in the mass spectrometry section later. 

Oomens J, Moehlig AR, Morton TH (2010) Infrared multiple photon dissociation (IRMPD) spectroscopy of the proton-bound dimer of 1-methylcytosine in the gas phase. J Phys Chem Lett 1 2891-2897... 

Activation of the vibrational energy of ions can also be induced by the absorption of IR radiations. A popular type of IR radiation source is far-IR laser. In fact, many molecules have a broad IR absorption band. The most widely used IR source is a continuous wave (c.w.) CO2 laser, with the wavelength of 10.6 pm. This wavelength corresponds to an energy of 0.3 eV per laser photon. Because decomposition of a chemical bond requires >1 eV, laser excitation has to extended over hundreds of milliseconds to allow ions to absorb multiple IR photons. This method is known as infrared multiphoton dissociation (IRMPD). Another type of similar technique is black-body infrared radiative dissociation... 

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