Transition Dipole Moment Measurements of Ultracold Photoassociated ^(85)Rb^(133)Cs Molecules by Depletion Spectroscopy

The transition dipole moments（TDMs） of ultracold85 Rb133 Cs molecules between the lowest vibrational ground level, （X^1Σ~＋（ v= 0, J= 1）, and the two excited rovibrational levels, 2~3Π0＋（v′= 10, J′= 2） and 2~1Π1（v′= 22,J′= 2）, are measured using depletion spectroscopy. The ground-state85 Rb133 Cs molecules are formed from cold mixed component atoms via the 2~3Π0-（ v= 11, J= 0） short-range level, then detected by time-of-flight mass spectrum. A home-made external-cavity diode laser is used as the depletion laser to couple the ground level and the two excited levels. Based on the depletion spectroscopy, the corresponding TDMs are then derived to be 3.5（2）×10^（-3）eαα and 1.6（1）×10^（-2）eαα, respectively, where 0）（60 represents the atomic unit of electric dipole moment. The enhance of TDM with nearly a factor of 5 for the 21Π1（v′= 22, J′= 2） excited level means that it has stronger coupling with the ground level. It is meaningful to find more levels with much more strong coupling strength by the represented depletion spectroscopy to realize direct stimulated Raman adiabatic passage transfer from scattering atomic states to deeply molecular states.

Single Molecule FRET Study of DNAG Quadruplex

The DNA G quadruplex formed by the human telomeric sequence is a potential target for novel anticancer drugs. We have investigated an intramolecular DNA G quadruplex using single molecule fluorescence resonance energy transfer and shown that individual folded quadruplexes can be identified. The mean proximity ratio measured at the single molecule level was consistent with ensemble measurement

Investigation on the Folding Mode of a Polymer Chain in a Spiral Crystal by Single Molecule Force Spectroscopy

Investigation on the folding mode of a single polymer chain in its crystal is significant to the understanding of the mechanism of the fundamental crystallization as well as the engineering of new polymer crystal-based materials. Herein, we use the combined techniques of atomic force microscopy （AFM） imaging and force spectroscopy to pull a single polyethylene oxide （PEO） chain out of its spiral crystal in amyl acetate. From these data, the folding mode of polymer chains in the spiral crystal has been reconstructed. We find that the stems tilt in the typical flat area, leading to the decrease in the apparent lamellar height. While in the area of screw dislocation, the lamellar height gradually increases in the range of several nanometers. These results indicate that the combined techniques present a novel tool to directly unravel the chain folding mode of spiral crystals at single-molecule level.

Collisional broadening of some 2~1Δ_g←B^1Π_u lines in Na_2 molecules by optical-optical double resonance spectroscopy

Using the optical-optical double resonance （OODR） technique, we have studied the collisional broadening of some 21△g←B1πu lines in Na2 molecules. A single line Ar＋ laser is used to pump the sodium dimers from thermally populated ground state X^1∑^＋g level to the intermediate B1πu state. Then, a single-mode diode laser is used to probe the doubly excited 21△g state. The broadening rate coefficient is determined from the slope of the total linewidth versus Ne density curve. We obtain the average value kbr = （1.1 ± 0.5）×10^-8 cm^3 8^-1. The collisional excitation transfer between rotational levels of the B1πu state （i.e.,B1πu（2,83/84） ←B1Ⅱu （2,82）） is also investigated. The rates can be determined from the relative intensities of the main peak and satellite lines, combined with a rate equation model. The rates of 1.25 × 106 and 1.07 × 106 s^-1 are obtained, respectively.

Fluorescence of Single Conjugated Chains of MEH-PPV Dispersed in Polymer Matrix: What Do We See in the Microscope?

It has been a mystery that the detected fluorescence intensity of single MEH-PPV molecules is much lower than expected based on their chain length.In this review,after re-evaluating of the literature data in the light of new specially designed experiments,we present a comprehensive explanation of this issue:The actual size of MEH-PPV molecules at single molecule level is much smaller than expected due to de-aggregation and chain scission,while static quenching("dark matter")also exists for large molecules,further reducing their brightness.

Stretching Elasticity and Flexibility of Single Polyformaldehyde Chain

In this work,the single-chain elasticity of polyformaldehyde(POM)is studied,for the first time,by employing atomic force microscopy(AFM)-based single molecule force spectroscopy(SMFS).We find that the single-chain elasticity of POM in a nonpolar organic solvent(nonane)can be described well by a theoretical model(QM-FRC model),when the rotating unit length is 0.144 nm(C―O bond length).After comparison,POM is more flexible than polystyrene(a typical polymer with C―C backbone)at the single-chain level,which is reasonable since the C―O bond has a lower rotation barrier than C―C bond.This result indicates that the flexibility of a polymer chain can be tuned by the C―O bond proportion in backbone,which casts new light on the rational design of new synthetic polymers in the future.