Photoexcitation processes of CH3OH: Rydberg states and photofragment fluorescence

Nee, J. B.; Suto, Masako; Lee, L.C.

doi:10.1016/0301-0104(85)80102-6

Cited by 59 publications

(43 citation statements)

References 21 publications

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“…The effect of flow rate on measured ion intensity with an [24,25] methanol, CH 3 OH (0.5 nm resolution); [26,27] and water, H 2 O (0.075 nm resolution) [28,29] APPI source and LC-MS has been reported previously using a Kr lamp [18], where the signal intensity can be seen to decrease at higher flow rates. Based on Beer's Law, light transmission is I/I 0 ϭ exp(Ϫ nx), which is a function of the wavelength-dependent photoabsorption cross-section, , molecular number density, n, and path length, x.…”

Section: Dependence Of Photoabsorption On Solvent Flowmentioning

confidence: 53%

APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

Short¹,

Cai²,

Syage³

2007

J. Am. Soc. Mass Spectrom.

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The technique of atmospheric pressure photoionization (APPI) has several advantages over electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), including efficient ionization of nonpolar or low charge affinity compounds, reduced susceptibility to ion suppression, high sensitivity, and large linear dynamic range. These benefits are greatest at low flow rates (i.e., Յ100 L/min), while at a higher flow, photon absorption and ion-molecule reactions become significant. Under certain circumstances, APPI signal and S/N have been observed to excel at higher flow, which may be due to a nonphotoionzation mechanism. To better understand APPI at higher flow rates, we have selected three lamps (Xe, Kr, and Ar) and four mobile phases typical for reverse-phase, high-pressure liquid chromatography: acetonitrile, methanol, (1:1) acetonitrile:water and (1:1) methanol:water. As test compounds, three polyaromatic hydrocarbons are studied: benzo[a]pyrene, indeno [1,2,3-c, d]pyrene and benz [a]anthracene. We find that solvent photoabsorption cross-section is not the only parameter in explaining relative signal intensity, but that solvent photo-ion chemistry can also play a significant role. Three conclusions from this investigation are: (1) [4,5]. Recent work has focused on the direct comparison of different sources (APPI, APCI, and ESI) with specific target compounds, e.g., polyaromatic hydrocarbons [6,7], hydrophobic peptides [8], pesticides [9,10], as well as fatty acids and lipids [4,5]. In many cases atmospheric pressure photoionization (APPI) [1,7] has demonstrated extended linear dynamic range [11], enhanced sensitivity and thus lower detection limits [6,9,[12][13][14][15], and reduced or no off-line sample cleanups [6,9] in comparison with direct APCI or ESI. Adding a dopant (dopant-assisted, DA) to the mobile phase in many cases can further increase sensitivity [2].A related analytical technique is atmospheric pressure laser ionization (APLI), which has shown excellent sensitivity for certain non-or low-polar compounds [3]. The enhanced sensitivity is a direct result of the high photon flux associated with a laser system, often several orders of magnitude higher than the noncoherent light sources, e.g., lamps used with APPI. The APLI source relies on one-color, two-photon (1 ϩ 1) resonantlyenhanced multiphoton ionization (REMPI), typically using a KrF excimer laser emitting light at 5.0 eV, efficiently ionizing nonpolar molecules. However, APLIis not yet widely used due to the large size, expense, and maintenance associated with the laser system. Furthermore, changing the wavelength of an excimer laser requires the replacement of the gas mixture and often re-tuning of the laser cavity, whereas with an APPI system, the wavelength can be changed by simply switching the lamp.To improve the capabilities of APPI for LC-MS, we have focused on the ion chemistry involved in and following the photoionization process. Although direct, single-photon ionization (SPI) of a compound [M] however, there is litt...

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Section: Dependence Of Photoabsorption On Solvent Flowmentioning

confidence: 53%

APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

Short¹,

Cai²,

Syage³

2007

J. Am. Soc. Mass Spectrom.

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“…VUV-absorption cross section as a function of photon wavelength (bottom X-axis) and VUV-photon energy (top X-axis) of pure CH 3 OH ice deposited at 8 K, black trace. The blue trace is the VUVabsorption cross-section spectrum of gas phase CH 3 OH adapted from Nee et al (1985). The fit, red trace, is the sum of two Gaussians, dashed trace.…”

Section: Solid Carbon Monoxidementioning

confidence: 99%

“…The VUV-absorption cross sections of CH 3 OH ice at 121.6 nm, 157.8 and 160.8 nm are 8.6 +0.7 −1.3 × 10 −18 cm 2 , 3.8 +0.3 −0.6 × 10 −18 cm 2 , and 2.9 +0.2 −0.4 × 10 −18 cm 2 . Gas phase data from Nee et al (1985) were used for comparison with our solid-phase spectrum, see Fig. 5.…”

Section: Solid Methanolmentioning

confidence: 99%

Vacuum-UV spectroscopy of interstellar ice analogs

Cruz-Díaz

Muñoz

Chen

et al. 2014

A&A

107

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Context. The vacuum-UV (VUV) absorption cross sections of most molecular solids present in interstellar ice mantles with the exception of H 2 O, NH 3 , and CO 2 have not been reported yet. Models of ice photoprocessing depend on the VUV absorption cross section of the ice to estimate the penetration depth and radiation dose, and in the past, gas phase cross section values were used as an approximation. Aims. We aim to estimate the VUV absorption cross section of molecular ice components. Methods. Pure ices composed of CO, H 2 O, CH 3 OH, NH 3 , or H 2 S were deposited at 8 K. The column density of the ice samples was measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120−160 nm (10.33−7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. Results. We provide VUV absorption cross sections of the reported molecular ices. Our results agree with those previously reported for H 2 O and NH 3 ices. Vacuum-UV absorption cross section of CH 3 OH, CO, and H 2 S in solid phase are reported for the first time. H 2 S presents the highest absorption in the 120−160 nm range. Conclusions. Our method allows fast and readily available VUV spectroscopy of ices without the need to use a synchrotron beamline. We found that the ice absorption cross sections can be very different from the gas-phase values, and therefore, our data will significantly improve models that simulate the VUV photoprocessing and photodesorption of ice mantles. Photodesorption rates of pure ices, expressed in molecules per absorbed photon, can be derived from our data.

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“…Numerous studies on the absorption spectra [8][9][10] of methanol have been carried out. Nee et al 8 reported an absorption spectrum of methanol in the region of 105-200 nm.…”

Section: Introductionmentioning

confidence: 99%

“…Nee et al 8 reported an absorption spectrum of methanol in the region of 105-200 nm. A weak continuous feature in the 165-195 nm region shown in the bottom panel of Fig.…”

Section: Introductionmentioning

confidence: 99%

Product pair correlation in CH₃OH photodissociation at 157 nm: the OH + CH₃channel

Chen

Eppink

Jiang

et al. 2011

Phys. Chem. Chem. Phys.

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The OH + CH 3 product channel for the photodissociation of CH 3 OH at 157 nm was investigated using the velocity map imaging technique with the detection of CH 3 radical products via (2+1) resonance-enhanced multiphoton ionization (REMPI). Images were measured for the CH 3 formed in the ground and excited states (v 2 = 0, 1, 2, and 3) of the umbrella vibrational mode and correlated OH vibrational state distributions were also determined. We find that the vibrational distribution of the OH fragment in the OH + CH 3 channel is clearly inverted. Anisotropic distributions for the CH 3 (v 2 = 0, 1, 2, and 3) products were also determined, which is indicative of a fast dissociation process for the C-O bond cleavage. A slower CH 3 product channel was also observed, that is assigned to a two-step photodissociation process, in which the first step is the production of a CH 3 O(X 2 E) radical via the cleavage of the O-H bond in CH 3 OH, followed by probe laser photodissociation of the nascent CH 3 O radicals yielding CH 3 (X 2 A 1 , v = 0) products.

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Photoexcitation processes of CH3OH: Rydberg states and photofragment fluorescence

Cited by 59 publications

References 21 publications

APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

Vacuum-UV spectroscopy of interstellar ice analogs

Product pair correlation in CH₃OH photodissociation at 157 nm: the OH + CH₃channel

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Photoexcitation processes of CH3OH: Rydberg states and photofragment fluorescence

Cited by 59 publications

References 21 publications

APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

APPI-MS: Effects of mobile phases and VUV lamps on the detection of PAH compounds

Vacuum-UV spectroscopy of interstellar ice analogs

Product pair correlation in CH3OH photodissociation at 157 nm: the OH + CH3channel

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Product

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Product pair correlation in CH₃OH photodissociation at 157 nm: the OH + CH₃channel