Photodissociation spectroscopy of Ca+–rare gas complexes

Abstract

Weakly bound complexes of the form Ca+–RG (RG=Ar, Kr, Xe) are prepared in a pulsed nozzle/laser vaporization cluster source and studied with mass-selected resonance enhanced photodissociation spectroscopy. The Ca+ (2P←2S) atomic resonance line is the chromophore giving rise to the molecular spectra in these complexes. Vibrationally resolved spectra are measured for these complexes in the corresponding 2Π←X 2Σ+ molecular electronic transition. These spectra are red shifted from the atomic resonance line, indicating that each complex is more strongly bound in its excited 2Π state than it is in the ground state. Vibronic progressions allow determination of the excited state vibrational constants: Ca+–Ar, ωe′=165 cm−1; Ca+–Kr, ωe′=149 cm−1; Ca+–Xe, ωe′=142 cm−1. Extrapolation of the excited state vibrational progressions, and combination with the known atomic asymptotes and spectral shifts, leads to determination of the ground state dissociation energies Ca+–Ar, D0″=700±100 cm−1 (0.09 eV); Ca+–Kr, D0″=1400±150 cm−1 (0.17 eV); Ca+–Xe, D0″=2300±150 cm−1 (0.29 eV). The spin–orbit splitting in the 2Π1/2,3/2 state for these complexes is larger than expected by comparison to the Ca+ atomic value.

Photodissociation spectroscopy of the Ca+–N2 complex

“…Our research group has an ongoing program in the investigation of metal ion interactions in weakly bound complexes through mass-selected photodissociation spectroscopy. [17][18][19][20][21][22][23][24][25][26]30 In the present work, we describe the first such photodissociation spectroscopy of Ca ϩ -N 2 .…”

“…Mass spectrometric techniques have produced abundant thermochemical data for metal ion-molecular complexes. [1][2][3] More recently, ab initio calculations [4][5][6][7][8][9] and optical spectroscopy studies [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]30 have become the focus for studying metal ion-ligand interactions. Our research group has an ongoing program in the investigation of metal ion interactions in weakly bound complexes through mass-selected photodissociation spectroscopy.…”

Ultraviolet-visible photodissociation spectra of Vn+Xe (n=5–8) cluster complex cations

“…A blueshift effect is surprising, since the inverse effect is generally observed. 18 The influence of a RG environment on the optical properties of clusters has been studied in matrix embedded clusters experiments. 19 For large clusters, a redshift occurs form krypton to xenon and can be explained in the framework of the Mie model of a sphere surrounded by a dielectric medium.…”

Spectroscopic characterization of excited Ca(4s4dδ 3DJ)RG(3Δ1,2) states (RG=Ar, Kr, Xe): No “heavy-atom” mixing of RG(ndδ) character into the wave functions

“…Consistent with no great increase in the molecular A SO constant on interaction of the Mg(3d␦) orbital with an Ar atom, the Mg(3s3d␦ 3 3 D J )•Ar͓ 3 ⌬͔ ←Mg(3s3p 3 P J )•Ar͓ 3 ⌸ 0 ϩ ,0 Ϫ͔ transitions could be adequately rotationally simulated 5 assuming Hund's case ''b'' character for the 3 ⌬ upper state, e.g., that A SO ϽBJ for the upperstate, consistent with A SO being at most a few hundredths of a cm Ϫ1 . In contrast, the Mg(3s3d␦ 3 …”

“…Spin-orbit ͑SO͒ effects in such complexes have also been extensively discussed with regard to mixing of orbital alignment bonding character, 1 predissociation, 1 and increases in the spin-orbit interaction by addition of ''heavy-atom'' RG character into nominally metal atom molecular orbitals. [1][2][3][4][5][6][7][8] It has been observed in several cases [1][2][3][4][5][6][7][8] of low-lying excited ''p '' and ''d '' states of M*•RG (M*ϭexcited metal atom or ion; RGϭrare-gas atom͒ van der Waals complexes that the molecular spin-orbit coupling constant, A SO , is sometimes much larger than that predicted from the atomic spin-orbit coupling constant of the M* excited multiplet states to which the M*•RG states correlate at large internuclear distances R. It now appears, at least for low-lying excited states M*, that such increases in A SO values usually result from direct heavy-atom mixing of RG(np ) valence character into the M*•RG wave functions at small internuclear distances R. This is consistent both with ͑i͒ the regular ͑rather than inverted͒ nature of the ⍀ multiplets, even with large increases in A SO , and ͑ii͒ the increase of A SO as vЈ decreases, consistent with greater mixing of RG(np ) valence character at smaller ''effective'' distances R. The direct mixing was first demonstrated by Buenker 8,9 for the LiAr( 2 ⌸) states, and has since been confirmed by others. 10,11 It is interesting to examine analogous cases of ''d␦'' outershell M* configurations in M*(nd␦)•RG(⌬) excited states to see if the same kind of direct ''heavy-atom'' mixing of RG(nd␦) character into the M*RG(⌬) wave functions can occur.…”