Multi-photon dissociation of CHBr3 at 248 and 193 nm: observation of the electronically excited CH() product

Lindner, Jörg; Ermisch, K.; Wilhelm, René

doi:10.1016/s0301-0104(98)00303-6

Cited by 21 publications

(34 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The setup for measuring the frequencies is shown in Figure 2. A pulsed supersonic beam of CH radicals, with a repetition rate of 10 Hz, is produced by photo-dissociation of CHBr 3 (96% purity stabilized in ethanol) in a 4 bar carrier gas of either He, Ne, Ar or Kr [46,47]. The measured mean speeds of the CH for each of these carrier gases are v 0 = 1710, 810, 570, and 420 m/s, and the translational temperature is typically TABLE II.…”

mentioning

confidence: 99%

A search for varying fundamental constants using hertz-level frequency measurements of cold CH molecules

et al. 2013

View full text Add to dashboard Cite

Many modern theories predict that the fundamental constants depend on time, position or the local density of matter. Here we develop a spectroscopic method for pulsed beams of cold molecules, and use it to measure the frequencies of microwave transitions in CH with accuracy down to 3 Hz. By comparing these frequencies with those measured from sources of CH in the Milky Way, we test the hypothesis that fundamental constants may differ between the high- and low-density environments of the Earth and the interstellar medium. For the fine structure constant we find Δα/α=(0.3±1.1) × 10−7, the strongest limit to date on such a variation of α. For the electron-to-proton mass ratio we find Δμ/μ=(−0.7±2.2) × 10−7. We suggest how dedicated astrophysical measurements can improve these constraints further and can also constrain temporal variation of the constants.

show abstract

mentioning

confidence: 99%

A search for varying fundamental constants using hertz-level frequency measurements of cold CH molecules

et al. 2013

View full text Add to dashboard Cite

show abstract

“…We produce a supersonic beam of CH by photodissociating bromoform. At 4 bar pressure, a carrier gas of He, Ne, Ar or Kr is bubbled through liquid bromoform (CHBr 3 , 96% purity stabilized in ethanol) and then expands through the 1 mmdiameter nozzle of a pulsed solenoid valve into a vacuum chamber (Lindner, Ermisch & Wilhelm 1998;Romanzin et al 2006). Light from an excimer laser (wavelength of 248 nm, duration 20 ns and energy up to 220 mJ) is focused in front of the nozzle to a spot 1 mm high (along y) and 4 mm wide (along z), where it dissociates the bromoform to produce the CH.…”

Section: Introductionmentioning

confidence: 99%

Measurement of the Lowest Millimeter-Wave Transition Frequency of the Ch Radical

Truppe

Hendricks

Hinds

et al. 2013

ApJ

View full text Add to dashboard Cite

The CH radical offers a sensitive way to test the hypothesis that fundamental constants measured on earth may differ from those observed in other parts of the universe. The starting point for such a comparison is to have accurate laboratory frequencies. Here we measure the frequency of the lowest millimetre-wave transition of CH, near 535 GHz, with an accuracy of 0.6 kHz. This improves the uncertainty by roughly two orders of magnitude over previous determinations and opens the way for sensitive new tests of varying constants.

show abstract

“…In the laboratory, the photolysis of bromoform has been extensively studied by using laser beams at various fixed wavelengths, mainly 266 nm, [2][3][4][5][6] 248 nm, 7 and 193 nm. 8 The Br, Br 2 , CHBr, CBr, CH͑X 2 ⌸͒, and CH͑A 2 ⌬͒ products have been probed by using various techniques, e.g., photofragment translational spectroscopy, 9,10 ion velocity imaging, 11 laser induced fluorescence ͑LIF͒, 3,[6][7][8]12 and cavity ring-down spectroscopy ͑CRDS͒. 13,14 All the above photolysis experiments were performed with significantly high laser fluences, resulting in multiphoton processes whose interpretation is not trivial.…”

Section: Introductionmentioning

confidence: 99%

“…This radical has been studied as an important reactant with other molecules. [3][4][5]8,[15][16][17] It has been characterized by several techniques, mostly by LIF, yielding information on the internal energy distribution in its ground state 2 or in its excited states 4,5,12,13,18,19 following 266, 248, and 193 nm photolysis. Depending on its nascent state population, production of this radical by 248 nm photolysis of CHBr 3 requires either a two-photon or a three-photon photolysis scheme for CH͑X 2 ⌸͒ or CH͑A 2 ⌬ , B 2 ⌺ − ͒, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…Depending on its nascent state population, production of this radical by 248 nm photolysis of CHBr 3 requires either a two-photon or a three-photon photolysis scheme for CH͑X 2 ⌸͒ or CH͑A 2 ⌬ , B 2 ⌺ − ͒, respectively. 12 Note that the multiphoton mechanism for CH production, involving either a direct or a sequential dissociation, is not well understood yet. However, progress has been made very recently by Chikan et al, 19 who have been able to explain the CHBr 3 dissociation mechanisms, following single and multiple photon excitations in the 10-20 eV energy range.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

CH radical production from 248nm photolysis or discharge-jet dissociation of CHBr3 probed by cavity ring-down absorption spectroscopy

Romanzin

Boyé-Péronne

Gauyacq

et al. 2006

The Journal of Chemical Physics

View full text Add to dashboard Cite

The A-X bands of the CH radical, produced in a 248 nm two-photon photolysis or in a supersonic jet discharge of CHBr(3), have been observed via cavity ring-down absorption spectroscopy. Bromoform is a well-known photolytic source of CH radicals, though no quantitative measurement of the CH production efficiency has yet been reported. The aim of the present work is to quantify the CH production from both photolysis and discharge of CHBr(3). In the case of photolysis, the range of pressure and laser fluences was carefully chosen to avoid postphotolysis reactions with the highly reactive CH radical. The CH production efficiency at 248 nm has been measured to be Phi=N(CH)N(CHBr(3))=(5.0+/-2.5)10(-4) for a photolysis laser fluence of 44 mJ cm(-2) per pulse corresponding to a two-photon process only. In addition, the internal energy distribution of CH(X (2)Pi) has been obtained, and thermalized population distributions have been simulated, leading to an average vibrational temperature T(vib)=1800+/-50 K and a rotational temperature T(rot)=300+/-20 K. An alternative technique for producing the CH radical has been tested using discharge-induced dissociation of CHBr(3) in a supersonic expansion. The CH product was analyzed using the same cavity ring-down spectroscopy setup. The production of CH by discharge appears to be as efficient as the photolysis technique and leads to rotationally relaxed radicals.

show abstract

Multi-photon dissociation of CHBr3 at 248 and 193 nm: observation of the electronically excited CH() product

Cited by 21 publications

References 27 publications

A search for varying fundamental constants using hertz-level frequency measurements of cold CH molecules

A search for varying fundamental constants using hertz-level frequency measurements of cold CH molecules

Measurement of the Lowest Millimeter-Wave Transition Frequency of the Ch Radical

CH radical production from 248nm photolysis or discharge-jet dissociation of CHBr3 probed by cavity ring-down absorption spectroscopy

Contact Info

Product

Resources

About