Measurement of Doppler effects in a cryogenic buffer-gas cell

Buffer-gas cooling is a universal cooling technique for molecules and used for various purposes. One of its ap- plications is using molecules inside a buffer-gas cell for low-temperature spectroscopy. Although a high-intensity signal is expected in the cell, complex molecular dynamics is a drawback for precise spectroscopy. In this study, we performed high-resolution absorption spectroscopy of low -J transitions in the òΠ(0, 0, 0)-˜X²Σ+(0, 0, 0) band of calcium monohydroxide (CaOH). CaOH molecules were produced by laser ablation in a copper cell and cooled to ∼5 K using helium buffer gas. We probed the Doppler effects in a buffer-gas cell by injecting counterpropagating lasers inside the cell. The time evolutions of the Doppler width and shift were simulated using a dedicated Monte Carlo simulation and compared with data

Low-J Transitions in A˜2Π(0,0,0)−X˜2Σ+(0,0,0) Band of Buffer-gas-cooled CaOH

Calcium monohydroxide radical (CaOH) is receiving an increasing amount of attention from the astrophysics community as it is expected to be present in the atmospheres of hot rocky super-Earth exoplanets as well as interstellar and circumstellar environments. Here, we report the high-resolution laboratory absorption spectroscopy on low-J transitions in A ˜ 2 Π ( 0 , 0 , 0 ) − X ˜ 2 Σ + ( 0 , 0 , 0 ) band of buffer-gas-cooled CaOH. In total, 40 transitions out of the low-J states were assigned, including 27 transitions that have not been reported in previous literature. The determined rotational constants for both ground and excited states are in excellent agreement with previous literature, and the measurement uncertainty for the absolute transition frequencies was improved by more than a factor of 3. This will aid future interstellar, circumstellar, and atmospheric identifications of CaOH. The buffer-gas-cooling method employed here is a particularly powerful method to probe low-J transitions and is easily applicable to other astrophysical molecules.</jats:p

High-resolution spectroscopy of buffer-gas-cooled phthalocyanine

For over five decades, studies in the field of chemical physics and physical chemistry have primarily aimed to understand the quantum properties of molecules. However, high-resolution rovibronic spectroscopy has been limited to relatively small and simple systems because translationally and rotationally cold samples have not been prepared in sufficiently large quantities for large and complex systems. In this study, we present high-resolution rovibronic spectroscopy results for large gas-phase molecules, namely, free-base phthalocyanine (FBPc). The findings suggest that buffer-gas cooling may be effective for large molecules introduced via laser ablation. High-resolution electronic spectroscopy, combined with other experimental and theoretical studies, will be useful in understanding the quantum properties of molecules. These findings also serve as a guide for quantum chemical calculations of large molecules

Clustering of OB-fold domains of the partner protease complexed with trimeric stomatin from Thermococcales.

International audienceThe C-terminal soluble domain of stomatin operon partner protein (STOPP) of the hyperthermophilic archaeon Pyrococcus horikoshii has an oligonucleotide binding-fold (OB-fold). STOPP lacks the conserved surface residues necessary for binding to DNA/RNA. A tryptophan (W) residue is conserved instead at the molecular surface. Solvent-accessible W residues are often found at interfaces of protein-protein complexes, which suggested the possibility of self-assembling of STOPP. Protein-protein interactions among the C-terminal soluble domains of STOPP PH1510 (1510-C) were then analyzed by chemical linking and blue native polyacrylamide gel electrophoresis (BN-PAGE) methods. These results suggest that the soluble domains of STOPP could assemble into homo-oligomers. Since hexameric subcomplex I from archaeal proteasome consists of coiled-coil segments and OB-fold domains, molecular modeling of 1510-C was performed using hexameric subcomplex I as a template. Although 1510-C is a comparatively small polypeptide consisting of approximately 60 residues, numerous salt bridges and hydrophobic interactions were observed in the predicted hexamer of 1510-C, suggesting the stability of the homo-oligomeric structure. This oligomeric property of STOPP may be favorable for triplicate proteolysis of the trimer of prokaryotic stomatin

Analysis on high-resolution spectrum of the S1–S0 transition of free-base phthalocyanine

A high-resolution absorption spectrum of the S-1-S-0 transition of free-base phthalocyanine was observed and analyzed with improved reliability. The spectrum, with a partially resolved rotational structure, was obtained by using the buffer-gas cooling technique and a single-mode tunable laser. Our new analysis reveals that the S-1 <- S-0 0(0)(0) band belongs to the a-type transition, where the electronic transition moment aligns parallel to the NH-HN direction, allowing the assignment of the S-1 state to B-1(3u). These results agree with a prior study using supersonic expansion and are well supported by theoretical calculations. Interestingly, the rotational constant B in the S-1 state, which is often smaller than that in the ground state for typical molecules, was found to be slightly larger than that in the S-0 (1)A(g) state. This suggests a change in the character of pi bonds with the electronic excitation

Analysis on high-resolution spectrum of the S1–S0 transition of free-base phthalocyanine

A high-resolution absorption spectrum of the S-1-S-0 transition of free-base phthalocyanine was observed and analyzed with improved reliability. The spectrum, with a partially resolved rotational structure, was obtained by using the buffer-gas cooling technique and a single-mode tunable laser. Our new analysis reveals that the S-1 <- S-0 0(0)(0) band belongs to the a-type transition, where the electronic transition moment aligns parallel to the NH-HN direction, allowing the assignment of the S-1 state to B-1(3u). These results agree with a prior study using supersonic expansion and are well supported by theoretical calculations. Interestingly, the rotational constant B in the S-1 state, which is often smaller than that in the ground state for typical molecules, was found to be slightly larger than that in the S-0 (1)A(g) state. This suggests a change in the character of pi bonds with the electronic excitation

High-resolution spectroscopy of buffer-gas-cooled phthalocyanine

For over five decades, studies in the field of chemical physics and physical chemistry have primarily aimed to understand the quantum properties of molecules. However, high-resolution rovibronic spectroscopy has been limited to relatively small and simple systems because translationally and rotationally cold samples have not been prepared in sufficiently large quantities for large and complex systems. In this study, we present high-resolution rovibronic spectroscopy results for large gas-phase molecules, namely, free-base phthalocya-nine (FBPc). The findings suggest that buffer-gas cooling may be effective for large molecules introduced via laser ablation. High-resolution electronic spectroscopy, combined with other experimental and theoretical studies, will be useful in understanding the quantum properties of molecules. These findings also serve as a guide for quantum chemical calculations of large molecules

High-resolution spectroscopy of buffer-gas-cooled phthalocyanine

High-resolution molecular spectroscopy provides invaluable insight into the quantum properties of molecules, but high-resolution rovibronic spectroscopy has largely been limited to relatively small systems owing to the difficulty in preparing translationally and rotationally cold samples for large and complex systems. Here, the authors demonstrate that buffer-gas cooling may be an effective strategy to obtain high-resolution rovibronic spectroscopy results for large gas-phase molecules