## 4 Conclusions  
In summary, we have developed a unique UV-FSRS setup with a home-built second harmonic bandwidth compressor output (\(\sim\)400 nm center wavelength, 1.5 ps fwhm) as the Raman pump and various broadband up-converted multicolor array (BUMA) sideband laser pulses (_ca._ 360--460 nm, fs) as the Raman probe to obtain the stimulated Raman spectrum. The BUMA signals in this work arise from SFG/SHG-based cascaded four-wave mixing processes in a thin BBO crystal. Two other Raman pump wavelengths are achieved using a tunable FSRS setup in the visible range and the resultant Stokes spectrum of 15 mM LD390 in methanol is \(>\)21 times weaker due to larger mismatch between the Raman pump wavelength and the electronic absorption peak frequency of the laser dye. This manifests the advantage of using tunable ps pulses to study molecules with different absorption profiles over a wide spectral range. The Raman spectrum of LD390 is collected over a \(\sim\)1400 cm\({}^{-1}\) detection window for the first time with vibrational mode assignments aided by _Gaussian_ DFT calculations. Using a \(\sim\)400 nm ps Raman pump, the anti-Stokes Raman spectrum turns out to be much stronger than the Stokes spectrum mainly due to pre-resonance enhancement involving the vibrational energy gap in _So_,  
Figure 4: **(a)** Comparison between the Stokes (red) and anti-Stokes (black) ground-state FSRS data for LD390 in methanol solution. The first-order UV-BUMA sideband S+1/S–1 on the fundamental pulse (FP)/white light (WL) side acts as the Raman probe for anti-Stokes/Stokes FSRS with the 402 nm Raman pump pulse, respectively. The frequency axes are calibrated and for direct spectral comparison, the anti-Stokes Raman shift axis as well as the Raman peak intensities are multiplied by –1. The insert tabulates the observed peak intensity ratios of several major vibrational modes between 600–1700 cm\({}^{-1}\). **(b)** The spectroscopic origin of the observed Raman intensity ratios can be understood by the molecular energy level diagram of LD390. Two characteristic vibrational modes are shown (vibrational quantum number \(\
u=1\)) with the relative energy differences between various Raman transition configurations depicted by colored vertical arrowed lines. The numbers in brackets represent effective Raman pump wavelengths in nm unit (see Section 3.3.).  
which is confirmed by the relative intensity ratio change between the low- and high-frequency vibrational modes.  
The versatile and compact approach of generating tunable probe pulses in the UV should make the FSRS technology more accessible to many laboratories for elucidation of molecular conformational dynamics in the electronic ground state, as well as excited state upon incorporation of a preceding fs photoexcitation pulse [10; 11; 13]. This methodology also paves the way to harness the broadband tunability of multi-color laser sidebands to study molecules that primarily absorb in the UV which include metal-organic complexes such as triphenylbismuth in methanol solution and biomolecules such as DNA and tyrosine derivatives in water. Related studies are currently underway.  
This project is supported by the Oregon State University Faculty Startup Research Grant and Research Equipment Reserve Fund (to [PERSON]) and the National Science Foundation (NSF) CAREER award (grant number CHE-1455353, to C.F. since Feb. 2015). We thank [PERSON] for the laser dye sample. We also acknowledge graduate research assistantship (to [PERSON]) from the NSF Center for Sustainable Materials Chemistry (grant number CHE-1102637).  
[PERSON] designed and supervised research; [PERSON], [PERSON], and [PERSON] contributed new analytic tools; [PERSON] and [PERSON] performed research; [PERSON], [PERSON], and [PERSON] analyzed data; and [PERSON] wrote the paper with discussions from all the authors.  
The authors declare no conflict of interest.